trimming excess errors from -Werror

[Danny Smith]

> 
> cc1plus: warnings being treated as errors
> 
> /cygdrive/e/gnu/gcc-4.3-20070511/libstdc++-v3/testsuite/17_int
> ro/headers/all_c++200x_compatibility.cc:1:
> error: -ffunction-sections may affect debugging on some targets
> 

This is actually a useful warning, since  -ffunction-sections not only
affects debugging but also adds unnecessary size to executables on
PE-COFF targets (and others where ld does not support --gc-sections).
One way to avoid is to add --enable-cxx-flags='-fno-function-sections
-fno-data-sections' to configure

Danny