Split mergeAvailabilityAttr out of handleAvailabilityAttr. This is important
for having a uniform logic for adding attributes to a decl. This in turn
is needed to fix the FIXME:

  // FIXME: This needs to happen before we merge declarations. Then,
  // let attribute merging cope with attribute conflicts.
  ProcessDeclAttributes(S, NewFD, D,
                        /*NonInheritable=*/false, /*Inheritable=*/true);

The idea is that mergeAvailabilityAttr will become a method. Once attributes
are processed before merging, it will be called from handleAvailabilityAttr to
handle multiple attributes in one decl:

void f(int) __attribute__((availability(ios,deprecated=3.0),
                           availability(ios,introduced=2.0)));

and from SemaDecl.cpp to handle multiple decls:

void f(int) __attribute__((availability(ios,deprecated=3.0)));
void f(int) __attribute__((availability(ios,introduced=2.0)));

As a bonus, use the new structure to diagnose incompatible availability
attributes added to different decls (see included testcases).

llvm-svn: 156269
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index d1cc73c..500de92 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -1633,6 +1633,13 @@
 /// attribute.
 static bool
 DeclHasAttr(const Decl *D, const Attr *A) {
+  // There can be multiple AvailabilityAttr in a Decl. Make sure we copy
+  // all of them. It is mergeAvailabilityAttr in SemaDeclAttr.cpp that is
+  // responsible for making sure they are consistent.
+  const AvailabilityAttr *AA = dyn_cast<AvailabilityAttr>(A);
+  if (AA)
+    return false;
+
   const OwnershipAttr *OA = dyn_cast<OwnershipAttr>(A);
   const AnnotateAttr *Ann = dyn_cast<AnnotateAttr>(A);
   for (Decl::attr_iterator i = D->attr_begin(), e = D->attr_end(); i != e; ++i)