Convert an if that never happens to an assert.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171354 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index 97fb50c..1e23ef7 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -7451,9 +7451,8 @@
     TSK = VD->getTemplateSpecializationKind();
 
   Linkage L = VD->getLinkage();
-  if (L == ExternalLinkage && getLangOpts().CPlusPlus &&
-      VD->getType()->getLinkage() == UniqueExternalLinkage)
-    L = UniqueExternalLinkage;
+  assert (!(L == ExternalLinkage && getLangOpts().CPlusPlus &&
+            VD->getType()->getLinkage() == UniqueExternalLinkage));
 
   switch (L) {
   case NoLinkage: