Auto merge of #1568 - ltratt:master, r=gnzlbg
Auto merge of #1568 - ltratt:master, r=gnzlbg

Add two missing pthread calls to the OpenBSD support.

These are shamelessly copied from the NetBSD support, whose prototypes in this regard are identical to OpenBSD's.

rust-lang/libc,rust-lang/libc,rust-lang/libc