gcc: don't clobber stamp-bits with a symlink to itself

Several versions of gcc have an issue in libstdc++v3 where the build may
clobber stamp-bits with a link to itself.  This doesn't manifest itself
on all systems.  On several Ubuntu systems, this doesn't appear to be a
problem, but it is an issue on Fedora 16 systems.

To fix the issue, we'll simply filter out stamp-bits from the symlinks
to be generated.