OpenBSD: Remove incorrect -pthread preprocessor define _POSIX_THREADS and replace with _REENTRANT. Also remove undef _POSIX_THREADS in phread.h.
OpenBSD: Remove incorrect -pthread preprocessor define _POSIX_THREADS and replace
with _REENTRANT. Also remove undef _POSIX_THREADS in phread.h.

Patch by Brad Smith!


git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@155535 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,apple/swift-clang,llvm-mirror/clang,llvm-mirror/clang,apple/swift-clang,llvm-mirror/clang