[driver] Emit an error when trying to use ARC on macosx earlier than 10.6

rdar://10459258

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@151706 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Driver/ToolChains.cpp b/lib/Driver/ToolChains.cpp
index 14c87d8..e125ab7 100644
--- a/lib/Driver/ToolChains.cpp
+++ b/lib/Driver/ToolChains.cpp
@@ -1019,6 +1019,10 @@
   return !isTargetIPhoneOS();
 }
 
+bool Darwin::SupportsObjCARC() const {
+  return isTargetIPhoneOS() || !isMacosxVersionLT(10, 6);
+}
+
 std::string
 Darwin_Generic_GCC::ComputeEffectiveClangTriple(const ArgList &Args,
                                                 types::ID InputType) const {