hopefully fix the build on windows.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@74977 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/System/Win32/DynamicLibrary.inc b/lib/System/Win32/DynamicLibrary.inc
index aa04268..ceecb5c 100644
--- a/lib/System/Win32/DynamicLibrary.inc
+++ b/lib/System/Win32/DynamicLibrary.inc
@@ -12,6 +12,7 @@
 //===----------------------------------------------------------------------===//
 
 #include "Win32.h"
+#include "llvm/System/RWMutex.h"
 
 #ifdef __MINGW32__
  #include <imagehlp.h>