This patch enables static linking of libstdc++ by default when building with WITH_STATIC_LIBS. This is already the current behaviour when using the buildbot script, but not for normal builds. This change makes Blender more portable (in particular to older systems), for anyone making static builds.
The increase in portability is significant. With static libstdc++, builds will run in RHEL/Centos 7, for example.
When building on GCC 4.9, linking against glibc 2.19, the build does not link against any newer symbols from 2.19, allowing it to run even on legacy enterprise systems running glibc 2.17. The only issue on the systems mentioned before, is libstdc++, which is 6.0.20 when building with gcc 4.9, while those systems are still using 6.0.19.
Of course one can always set the linker flag manually, but this patch just makes it easier for anyone targetting those (very popular) systems.
So if there are no objections, can I commit it?