trimming excess errors from -Werror

[Benjamin Kosnik]

> 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

libstdc++ configure is already probing to see if the target supports the 
use of this flag without errors. It thinks AIX and cygwin can use this 
flag without errors or warnings, which is clearly wrong.

So, something needs to be fixed.

Can you try

int i;

with "-Werror -ffunction-sections -fdata-sections" and see if you get an 
error with g++?

if not, can you try

int i;
void bar() { }

with the same flags and see if you get the error?

best,
benjamin