bug and fix ~ media-sound/moc-2.6_alpha3-r6 fails to compile: configure: error: I dont know how to compile pthreads

https://bugs.gentoo.org/831179

Hallo. This issue is encountered on an LLVM system, compiling with clang.

There is an issue in the `ax_pthread.m4`

I created a patch which allows moc to compile with clang in Gentoo, but this issue is also fixed in the upstream ax_pthread.m4.