Don't propagate the 'availability' attribute through declaration
merging for overrides. One might want to make a method's availability
in a superclass different from that of its subclass. Fixes
<rdar://problem/10166223>.

llvm-svn: 140406
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 3878341..da0fa3e 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1493,9 +1493,11 @@
   for (specific_attr_iterator<InheritableAttr>
        i = oldDecl->specific_attr_begin<InheritableAttr>(),
        e = oldDecl->specific_attr_end<InheritableAttr>(); i != e; ++i) {
-    // Ignore deprecated and unavailable attributes if requested.
+    // Ignore deprecated/unavailable/availability attributes if requested.
     if (!mergeDeprecation &&
-        (isa<DeprecatedAttr>(*i) || isa<UnavailableAttr>(*i)))
+        (isa<DeprecatedAttr>(*i) || 
+         isa<UnavailableAttr>(*i) ||
+         isa<AvailabilityAttr>(*i)))
       continue;
 
     if (!DeclHasAttr(newDecl, *i)) {