Fix -Wmissing-variable-declarations regression.

This issue was introduced in r181677.

PR17349.

llvm-svn: 191339
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 92400df..fa51aa4 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -8683,7 +8683,7 @@
   }
 
   if (var->isThisDeclarationADefinition() &&
-      var->isExternallyVisible() &&
+      var->isExternallyVisible() && var->hasLinkage() &&
       getDiagnostics().getDiagnosticLevel(
                        diag::warn_missing_variable_declarations,
                        var->getLocation())) {