libc/glibc: fix building for seemingly native toolchains

Build glibc with -O2 as a fix/workaround to building
seemingly-native toolchains.

See:
- docs/overview.txt
- docs/known-issues.txt
- http://sourceware.org/ml/crossgcc/2009-09/msg00055.html

reporter_name="Nye Liu"

reporter_url="http://sourceware.org/ml/crossgcc/2008-10/msg00046.html"

reporter_comment=""