Cleanup handling of UniqueExternalLinkage.

This patch renames getLinkage to getLinkageInternal. Only code that
needs to handle UniqueExternalLinkage specially should call this.

Linkage, as defined in the c++ standard, is provided by
getFormalLinkage. It maps UniqueExternalLinkage to ExternalLinkage.

Most places in the compiler actually want isExternallyVisible, which
handles UniqueExternalLinkage as internal.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@181677 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CodeGenModule.cpp b/lib/CodeGen/CodeGenModule.cpp
index 695048e..0736879 100644
--- a/lib/CodeGen/CodeGenModule.cpp
+++ b/lib/CodeGen/CodeGenModule.cpp
@@ -1763,7 +1763,7 @@
     return;
 
   // Must have internal linkage and an ordinary name.
-  if (!D->getIdentifier() || D->getLinkage() != InternalLinkage)
+  if (!D->getIdentifier() || D->getFormalLinkage() != InternalLinkage)
     return;
 
   // Must be in an extern "C" context. Entities declared directly within