Fix __SIZEOF_PTHREAD_MUTEX_T for mips
Fix __SIZEOF_PTHREAD_MUTEX_T for mips

This was changed when emscripten test support was added

rust-lang/libc,rust-lang/libc,cactorium/libc,rust-lang-nursery/libc,cactorium/libc,rust-lang-nursery/libc,rust-lang-nursery/libc,cactorium/libc,rust-lang/libc