From my build log:

cc -c -I../../../.. -I../../.. -I../.. -DXTHREADS -I/usr/include/gtk-2.0
-I/usr/lib/gtk-2.0/include -I/usr/X11R6/include -I/usr/include/atk-1.0
-I/usr/include/pango-1.0 -I/usr/include/freetype2 -I/usr/include/glib-2.0
-I/usr/lib/glib-2.0/include   -I/usr/include/libxml2   -DGUI_SOURCES
-DCURDIR=src/ui/gtk/gtk2 -O2 -g -Wall -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
-D_FILE_OFFSET_BITS=64  downloads.c
In file included from downloads.c:30:
pbarcellrenderer.h:57:1: warning: "GTK_TYPE_CELL_RENDERER_PROGRESS" redefined
In file included from /usr/include/gtk-2.0/gtk/gtk.h:53,
                 from ../../gtk/gui.h:31,
                 from downloads.c:26:
/usr/include/gtk-2.0/gtk/gtkcellrendererprogress.h:34:1: warning: this is the
location of the previous definition
In file included from downloads.c:30:
pbarcellrenderer.h:62: error: redefinition of `GtkCellRendererProgress'
/usr/include/gtk-2.0/gtk/gtkcellrendererprogress.h:41: error:
`GtkCellRendererProgress' previously declared here
pbarcellrenderer.h:63: error: redefinition of `GtkCellRendererProgressClass'
/usr/include/gtk-2.0/gtk/gtkcellrendererprogress.h:42: error:
`GtkCellRendererProgressClass' previously declared here
pbarcellrenderer.h:66: error: redefinition of `struct _GtkCellRendererProgress'
pbarcellrenderer.h:71: error: redefinition of `struct _GtkCellRendererProgressClass'
make[5]: *** [downloads.o] Error 1
make[5]: Leaving directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk/gtk2'
make[4]: *** [gtk2/libgtk2.a] Error 2
make[4]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk'
make[3]: *** [ui/gtk/libgtkx.a] Error 2
make[3]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src'
Installing in pixmaps...
make[3]: Entering directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/pixmaps'+ test -d
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ /usr/bin/install -d
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
case '-w' in *[i]*) set +e;; esac;              \
(set -x; test -d
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
|| \
        /usr/bin/install -d
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps);
\
for i in arrow_down.xpm arrow_up.xpm booklib.xpm booksha.xpm bookshav.xpm
clanbomber_red.xpm clanbomber_yellow.xpm download.xpm exit.xpm filter.xpm
firewall.xpm firewall_punchable.xpm firewall_tcp.xpm firewall_udp.xpm
firewall_udp_punchable.xpm freeze.xpm icon.xpm leaf.xpm legacy.xpm
no_firewall.xpm offline.xpm online.xpm save.xpm smallserver.xpm
stock_form-time-field-16.xpm thaw.xpm ultra.xpm upload.xpm warning.xpm; do \
        (set -x; ../install -c -m 444 $i
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps);
\
done
+ test -d
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 arrow_down.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 arrow_up.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 booklib.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 booksha.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 bookshav.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 clanbomber_red.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 clanbomber_yellow.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 download.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 exit.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 filter.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 firewall.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 firewall_punchable.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 firewall_tcp.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 firewall_udp.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 firewall_udp_punchable.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 freeze.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 icon.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 leaf.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 legacy.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 no_firewall.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 offline.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 online.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 save.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 smallserver.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 stock_form-time-field-16.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 thaw.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 ultra.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 upload.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
+ ../install -c -m 444 warning.xpm
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/gtk-gnutella/pixmaps
install in pixmaps done.
make[3]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/pixmaps'
Installing in po...
make[3]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/po'
/usr/bin/install -d /home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share
installing de.gmo as
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/locale/de/LC_MESSAGES/gtk-gnutella.mo
installing es.gmo as
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/locale/es/LC_MESSAGES/gtk-gnutella.mo
installing fr.gmo as
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/locale/fr/LC_MESSAGES/gtk-gnutella.mo
installing ja.gmo as
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/locale/ja/LC_MESSAGES/gtk-gnutella.mo
installing nl.gmo as
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/locale/nl/LC_MESSAGES/gtk-gnutella.mo
installing hu.gmo as
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/locale/hu/LC_MESSAGES/gtk-gnutella.mo
make[3]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/po'
make[2]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95'
make[1]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95'
/usr/bin/make install.man INSTALL_PREFIX=`pwd`/debian/tmp
make[1]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95'
make[2]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95'
Installing man pages in src...
make[3]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src'
case '-w' in *[i]*) set +e;; esac;              \
(set -x; test -d
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/man/man1 || \
        /usr/bin/install -d
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/man/man1); \
../install -c -m 444 gtk-gnutella.man
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/man/man1/gtk-gnutella.1
+ test -d /home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/man/man1
+ /usr/bin/install -d
/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/share/man/man1
make[4]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src'
Installing man pages in src/core...
make[5]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/core'
make[5]: Nothing to be done for `install.man'.
make[5]: Leaving directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/core'Installing man pages in
src/lib...
make[5]: Entering directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/lib'make[5]: Nothing to be done
for `install.man'.
make[5]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/lib'
Installing man pages in src/ui...
make[5]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui'
make[6]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui'
Installing man pages in src/ui/gtk...
make[7]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk'
make[8]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk'
Installing man pages in src/ui/gtk/gtk1...
make[9]: Entering directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk/gtk1'
make[9]: Nothing to be done for `install.man'.
make[9]: Leaving directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk/gtk1'
Installing man pages in src/ui/gtk/gtk2...
make[9]: Entering directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk/gtk2'
make[9]: Nothing to be done for `install.man'.
make[9]: Leaving directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk/gtk2'
make[8]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk'
make[7]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui/gtk'
make[6]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui'
make[5]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/ui'
Installing man pages in src/if...
make[5]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/if'
make[6]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/if'
Installing man pages in src/if/bridge...
make[7]: Entering directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/if/bridge'
make[7]: Nothing to be done for `install.man'.
make[7]: Leaving directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/src/if/bridge'
make[6]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/if'
make[5]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src/if'
make[4]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src'
make[3]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/src'
Installing man pages in pixmaps...
make[3]: Entering directory
`/home/daniel/porting/tmp/gtk-gnutella-0.95/pixmaps'make[3]: Nothing to be done
for `install.man'.
make[3]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/pixmaps'
Installing man pages in po...
make[3]: Entering directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/po'
make[3]: Nothing to be done for `install.man'.
make[3]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95/po'
make[2]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95'
make[1]: Leaving directory `/home/daniel/porting/tmp/gtk-gnutella-0.95'
# install .desktop
install -D -m 0644 gtk-gnutella.desktop
`pwd`/debian/tmp/usr/share/applications/gtk-gnutella.desktop
# strip binary
strip --remove-section=.comment --remove-section=.note
`pwd`/debian/tmp/usr/bin/gtk-gnutella
strip:
'/home/daniel/porting/tmp/gtk-gnutella-0.95/debian/tmp/usr/bin/gtk-gnutella': No
such file

I'll go back and check debian/control's Build-Depends and the source depending
on gtk2.