Comment 49 for bug 1401788

add --enable-debug=full, make fail.
make[4]: Leaving directory `/GFX/build/component/Xf86_video_intel/xf86-video-intel/src/sna/fb'
make[4]: Entering directory `/GFX/build/component/Xf86_video_intel/xf86-video-intel/src/sna'
  CC blt.lo
  CC kgem.lo
  CC sna_accel.lo
sna_accel.c: In function 'sna_poly_zero_line_blt':
sna_accel.c:8920:7: warning: variable 'degenerate' set but not used [-Wunused-but-set-variable]
  bool degenerate = true;
       ^
  CC sna_acpi.lo
  CC sna_blt.lo
  CC sna_composite.lo
  CC sna_cpu.lo
  CC sna_damage.lo
  CC sna_display.lo
In file included from sna.h:112:0,
                 from sna_display.c:43:
sna_display.c: In function 'sna_output_backlight_off':
sna_display.c:630:33: error: 'output' undeclared (first use in this function)
  DBG(("%s(%s)\n", __FUNCTION__, output->name));
                                 ^
fb/fb.h:43:21: note: in definition of macro 'DBG'
 #define DBG(x) LogF x
                     ^
sna_display.c:630:33: note: each undeclared identifier is reported only once for each function it appears in
  DBG(("%s(%s)\n", __FUNCTION__, output->name));
                                 ^
fb/fb.h:43:21: note: in definition of macro 'DBG'
 #define DBG(x) LogF x
                     ^
sna_display.c: In function 'sna_output_backlight_on':
sna_display.c:638:33: error: 'output' undeclared (first use in this function)
  DBG(("%s(%s)\n", __FUNCTION__, output->name));
                                 ^
fb/fb.h:43:21: note: in definition of macro 'DBG'
 #define DBG(x) LogF x
                     ^
sna_display.c:642:17: warning: declaration of 'output' shadows previous non-variable [-Wshadow]
   xf86OutputPtr output = sna_output->base;
                 ^
make[4]: *** [sna_display.lo] Error 1
make[4]: Leaving directory `/GFX/build/component/Xf86_video_intel/xf86-video-intel/src/sna'
make[3]: *** [all-recursive] Error 1
make[3]: Leaving directory `/GFX/build/component/Xf86_video_intel/xf86-video-intel/src/sna'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/GFX/build/component/Xf86_video_intel/xf86-video-intel/src'
make[1]: *** [all-recursive] Error 1
make[1]: Leaving directory `/GFX/build/component/Xf86_video_intel/xf86-video-intel'
make: *** [all] Error 2