Add a portable wrapper for reader-writer locks.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73545 91177308-0d34-0410-b5e6-96231b3b80d8

lib/System/Unix/RWMutex.inc

@@ -0,0 +1,43 @@
+//= llvm/System/Unix/RWMutex.inc - Unix Reader/Writer Mutual Exclusion Lock  =//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// This file implements the Unix specific (non-pthread) RWMutex class.
+//
+//===----------------------------------------------------------------------===//
+
+//===----------------------------------------------------------------------===//
+//=== WARNING: Implementation here must contain only generic UNIX code that
+//===          is guaranteed to work on *all* UNIX variants.
+//===----------------------------------------------------------------------===//
+
+namespace llvm {
+
+using namespace sys;
+
+RWMutex::RWMutex() { }
+
+RWMutex::~RWMutex() { }
+
+bool RWMutex::reader_acquire() {
+  return true;
+}
+
+bool RWMutex::reader_release() {
+  return true;
+}
+
+bool RWMutex::writer_acquire() {
+  return true;
+}
+
+bool RWMutex::writer_release() {
+  return true;
+}
+
+}