Add a minimal unwind.h that knows how to forward to the system one in systems
that have it in /usr/include (only OS X Lion so far).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@146140 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Headers/CMakeLists.txt b/lib/Headers/CMakeLists.txt
index 771cfcd..af03830 100644
--- a/lib/Headers/CMakeLists.txt
+++ b/lib/Headers/CMakeLists.txt
@@ -24,6 +24,7 @@
   x86intrin.h
   xmmintrin.h
   cpuid.h
+  unwind.h
   )
 
 set(output_dir ${LLVM_BINARY_DIR}/lib/clang/${CLANG_VERSION}/include)