[-cxx-abi microsoft] Mangle local TagDecls appropriately

Summary:
When selecting a mangling for an anonymous tag type:
- We should first try it's typedef'd name.
- If that doesn't work, we should mangle in the name of the declarator
  that specified it as a declaration specifier.
- If that doesn't work, fall back to a static mangling of
  <unnamed-type>.

This should make our anonymous type mangling compatible.

This partially fixes PR16994; we would need to have an implementation of
scope numbering to get it right (a separate issue).

Reviewers: rnk, rsmith, rjmccall, cdavis5x

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1540

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@190892 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index a2e05e0..beffe41 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -8814,13 +8814,21 @@
   if (DS.isTypeSpecOwned())
     Decls.push_back(DS.getRepAsDecl());
 
+  DeclaratorDecl *FirstDeclaratorInGroup = 0;
   for (unsigned i = 0, e = Group.size(); i != e; ++i)
-    if (Decl *D = Group[i])
+    if (Decl *D = Group[i]) {
+      if (DeclaratorDecl *DD = dyn_cast<DeclaratorDecl>(D))
+        if (!FirstDeclaratorInGroup)
+          FirstDeclaratorInGroup = DD;
       Decls.push_back(D);
+    }
 
   if (DeclSpec::isDeclRep(DS.getTypeSpecType())) {
-    if (const TagDecl *Tag = dyn_cast_or_null<TagDecl>(DS.getRepAsDecl()))
+    if (TagDecl *Tag = dyn_cast_or_null<TagDecl>(DS.getRepAsDecl())) {
       HandleTagNumbering(*this, Tag);
+      if (!Tag->hasNameForLinkage() && !Tag->hasDeclaratorForAnonDecl())
+        Tag->setDeclaratorForAnonDecl(FirstDeclaratorInGroup);
+    }
   }
 
   return BuildDeclaratorGroup(Decls, DS.containsPlaceholderType());