combined enable-build-with-cxx bootstrap comparison failure

[Ralf Wildenhues]

If I combine GCC and binutils-gdb, bootstrap, enable gold, use
--enable-build-with-cxx:

configured by ../src/configure, generated by GNU Autoconf 2.64,
  with options " '-C' '--enable-maintainer-mode' '--enable-objc-gc' '--enable-libssp' '--enable-sim' '--enable-gold' '--enable-build-with-cxx' 'CC=/home/ralf/recent/bin/gcc' 'CXX=/home/ralf/recent/bin/g++' '--enable-languages=c,c++,fortran,java,objc,obj-c++'"

and a very recent GCC as $build compiler:
| gcc (GCC) 4.5.0 20090916 (experimental)

GMP 4.2.1, MPFR 3.0.0.dev, then I get a bootstrap comparison failure:

Comparing stages 2 and 3
warning: gcc/cc1obj-checksum.o differs
warning: gcc/cc1-checksum.o differs
warning: gcc/cc1plus-checksum.o differs
warning: gcc/cc1objplus-checksum.o differs
Bootstrap comparison failure!
gold/i386.o differs
gold/stringpool.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/libsupc++/eh_alloc.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/libsupc++/eh_globals.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/libsupc++/vec.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/mt_allocator.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/system_error.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/future.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/pool_allocator.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/basic_file.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/atomic.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/locale.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/mt_allocator.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/system_error.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/future.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/pool_allocator.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/basic_file.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/atomic.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/locale.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/locale_init.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/.libs/debug.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/locale_init.o differs
x86_64-unknown-linux-gnu/libstdc++-v3/src/debug.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/libsupc++/eh_alloc.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/libsupc++/eh_globals.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/libsupc++/guard.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/libsupc++/vec.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/mt_allocator.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/system_error.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/future.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/pool_allocator.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/basic_file.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/atomic.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/locale.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/mt_allocator.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/system_error.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/future.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/pool_allocator.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/basic_file.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/atomic.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/locale.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/locale_init.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/.libs/debug.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/locale_init.o differs
x86_64-unknown-linux-gnu/32/libstdc++-v3/src/debug.o differs
make[2]: *** [compare] Error 1

Now, what do I do to (help) debug this?  Open a PR?  Attach some of the
object files (which)?  How do I know this is the same as (or different
from) <http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41340>?

Note the comparison failure does not occur if I
- don't build from a combined tree (i.e., using binutils for Debian
  2.18.0.20080103), or
- turn off both of --enable-gold --enable-build-with-cxx (I cannot turn
  off the latter without turning off the former, see mail on gcc-patches.)

Thanks,
Ralf