Modify the cross-compiling shell script to configure GCC for building GCC with C++ support when building its second (i.e., final) version.
Compiling a most-trivial C++ program used to work with GCC 4.2 and 4.3 (and the resulting binaries would also work), but linking fails with GCC SVN trunk:
$ $TARGET-g++ -Wall a.cc -lpthread
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__multf3'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__fixunstfsi'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__subtf3'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__divtf3'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__copysigntf3'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__addtf3'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__lttf2'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__floatsitf'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__netf2'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__floatunsitf'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__eqtf2'
/home/thomas/tmp/gnu-0/lib/gcc/i586-pc-gnu/4.4.0/../../../../i586-pc-gnu/lib/libgcc_s.so: undefined reference to `__fabstf2'
collect2: ld returned 1 exit status
Whether this defect report also applies to a natively-build GCC from SVN trunk has not yet been checked.
Thomas Schwinge suspects the problem to be a configuration issue of a GCC helper library, whose configuration setup has changed after GCC 4.3.
The need for -lpthread is another story. See the Debian glibc patches
repository for details.