gcc: fix libgomp to not use initial-exec

Only apply w/musl since while it's wrong everywhere it apparently
hasn't broken things entirely w/glibc so keep things as they were.

Patch regenerated from original so that it applies
which isn't saying much since it's simple :).

Source:

https://patchwork.ozlabs.org/patch/154298/

IRC chat on #musl with Rich and others endorses this,
at least at the conceptual level of no shared library
should be using initial-exec TLS.

Fixes various uses of libgomp that previously crashed (before 1.1.20)
or encounter errors (post-1.1.20), such as pythonPackages.cython .