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: https://llvm.org/svn/llvm-project/cfe/trunk@155535 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Basic/Targets.cpp b/lib/Basic/Targets.cpp
index 1eceaaa..dd2a89a 100644
--- a/lib/Basic/Targets.cpp
+++ b/lib/Basic/Targets.cpp
@@ -365,7 +365,7 @@
     DefineStd(Builder, "unix", Opts);
     Builder.defineMacro("__ELF__");
     if (Opts.POSIXThreads)
-      Builder.defineMacro("_POSIX_THREADS");
+      Builder.defineMacro("_REENTRANT");
   }
 public:
   OpenBSDTargetInfo(const std::string &triple)