Bug#748681: musl libc weak symbol usage incompatible with GCC 4.9

[Kevin Bortis <pkgs@bortis.ch>]

The bug was fixed by upstream gcc and is now found in the GCC-4.9 source tree.

Upstream bug report: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=61144

Upstream patch: https://gcc.gnu.org/viewcvs/gcc/branches/gcc-4_9-branch/gcc/varpool.c?r1=215896&r2=215895&pathrev=215896