Problems bootstrapping libgfortran in trunk on x86_64 Linux

[Roger Hill-Cottingham <eesrjhc at bath dot ac dot uk>]

I have a weekly cron script that gets trunk from svn and bootstraps C,
C++ and gfortran in a clean directory. This has worked fine for some
time (over a year) but the last one to succeed was:

$ gfortran --version
GNU Fortran 95 (GCC) 4.3.0 20061029 (experimental)

Since then, I get the following error when building libgfortran:

.
.
.

.libs/in_unpack_generic.o: In function `strtod':
/usr/include/gentoo-multilib/amd64/stdlib.h:330: multiple definition of `atof'
.libs/environ.o:/usr/include/gentoo-multilib/amd64/stdlib.h:330: first defined here
collect2: ld returned 1 exit status
make[3]: *** [libgfortran.la] Error 1
make[3]: Leaving directory `/MHz/roger/src/gcc-svn/build_hertz/x86_64-unknown-linux-gnu/libgfortran'
make[2]: *** [all] Error 2
make[2]: Leaving directory `/MHz/roger/src/gcc-svn/build_hertz/x86_64-unknown-linux-gnu/libgfortran'
make[1]: *** [all-target-libgfortran] Error 2
make[1]: Leaving directory `/MHz/roger/src/gcc-svn/build_hertz'
make: *** [bootstrap] Error 2

There are 5821 of these error messages, all complaining about multiple
definitions of something that is included from the same include file
in different object files. 

I know that others are not getting this problem on my platform as I
seem many instances of successful regression testing on
x86_64-unknown-linux-gnu reported on this mailing list, so there must
be something I'm doing wrong, or not upgraded. However, I've looked
through all the requirements for building gcc in .../trunk/gcc/doc/*
and I have either the same or newer versions of all the tools needed
to build gcc.

Some system info:

$ uname -a
Linux hertz 2.6.17-gentoo-r4 #1 SMP Thu Aug 24 16:20:25 BST 2006 x86_64 AMD Opteron(tm) Processor 844 GNU/Linux

$ ld --version
GNU ld version 2.16.1

Configured with:
../trunk/configure --prefix=/usr/local/gcc-svn --enable-languages=c,c++,fortran --disable-multilib

Does anybody recognise this problem? Is there any other information
you need from me to help?

BTW, I have a i686 machine, also running Gentoo Linux with the same
tools installed, that can bootstrap from the same trunk without
problems.

Best wishes,
Roger.