Do not emit duplicate global initializers for template static data members inside namespaces

A quirk of AST representation leads to class template static data member
definitions being visited twice during Clang IRGen resulting in
duplicate (benign) initializers.

Discovered while investigating a possibly-related debug info bug tickled
by the duplicate emission of these members & their associated debug
info.

With thanks to Richard Smith for help investigating, understanding, and
helping with the fix.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@189996 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 3b28d9d..6c12671 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -2761,8 +2761,13 @@
 /// EmitNamespace - Emit all declarations in a namespace.
 void CodeGenModule::EmitNamespace(const NamespaceDecl *ND) {
   for (RecordDecl::decl_iterator I = ND->decls_begin(), E = ND->decls_end();
-       I != E; ++I)
+       I != E; ++I) {
+    if (const VarDecl *VD = dyn_cast<VarDecl>(*I))
+      if (VD->getTemplateSpecializationKind() != TSK_ExplicitSpecialization &&
+          VD->getTemplateSpecializationKind() != TSK_Undeclared)
+        continue;
     EmitTopLevelDecl(*I);
+  }
 }
 
 // EmitLinkageSpec - Emit all declarations in a linkage spec.