gcc-4.5 fails to cross-build

[Wookey]

Crossbuilding gcc-4.5-base using xdeb in a natty chroot fails.

The build command is:
xdeb --only-explicit -a armel --prefer-apt --apt-source --debug --force-rebuild gcc-4.5
using xdeb 0.6.5~crosstoolsppa from https://launchpad.net/~linaro-foundations/+archive/cross-build-tools

The actual build command xdeb issues is:
debuild --no-lintian -eUSER -eCONFIG_SITE=/etc/dpkg-cross/cross-config.armel -eDEB_BUILD_OPTIONS=nocheck -eGTEST_INCLUDEDIR=/usr/arm-linux-gnueabi/include -eGTEST_LIBDIR=/usr/arm-linux-gnueabi/lib -ePKG_CONFIG_LIBDIR=/usr/arm-linux-gnueabi/lib/pkgconfig:/usr/arm-linux-gnueabi/share/pkgconfig:/usr/share/pkgconfig -eDH_VERBOSE=1 -aarmel -b -uc -us -tc

The final erorr is:

gcc -c -DIN_GCC -DGENERATOR_FILE -I. -Ibuild -I../../src/gcc -I../../src/gcc/build -I../../src/gcc/../include -I../../s$
                -o build/genmddeps.o ../../src/gcc/genmddeps.c
In file included from ../../src/gcc/rtl.h:28:0,
                 from ../../src/gcc/read-rtl.c:30:
../../src/gcc/real.h:83:13: error: size of array 'test_real_width' is negative

[Wookey (wookey)]

To easily reproduce the build environment in which this bug was discovered follow the HOWTO here:
https://wiki.linaro.org/Platform/DevPlatform/CrossCompile/CrossBuildNano

Setting 'buildlist' to just be the one line:
gcc-4.5-base

would mean it only builds this package and not lots of others too.

[Wookey (wookey)]

This seems designed to catch wrong size definitions with negative value:
/* Verify the guess. */
extern char test_real_width
  [sizeof(REAL_VALUE_TYPE) <= REAL_WIDTH*sizeof(HOST_WIDE_INT) ? 1 : -1];

everything seems derived from HOST_BITS_PER_LONG and HOST_BITS_PER_WIDE_INT