Fix include of config.h that was incorrectly changed in r331184

The RWMutex implementation depends on config.h macros (specifically
HAVE_PTHREAD_H and HAVE_PTHREAD_RWLOCK_INIT), so we need to be
including it and not just llvm-config.h here or we fall back to a much
slower implementation.

llvm-svn: 331487

Author: bogner

llvm/lib/Support/RWMutex.cpp

@@ -13,7 +13,7 @@
 
 #include "llvm/Support/Allocator.h"
 #include "llvm/Support/RWMutex.h"
-#include "llvm/Config/llvm-config.h"
+#include "llvm/Config/config.h"
 
 //===----------------------------------------------------------------------===//
 //=== WARNING: Implementation here must contain only TRULY operating system