Use isExternalLinkage instead of hasExternalLinkage.

Having these not be the same makes an easy to misuse API. We should audit the
uses and probably rename to something like

foo->hasExternalLinkage():
  The c++ standard one. That is UniqueExternalLinkage or ExternalLinkage.

foo->hasUniqueExternalLinkage():
  Is UniqueExternalLinkage.

foo->hasCogeGenExternalLinkage():
  Is ExternalLinkage.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@178768 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index af0b2bb..7a537f0 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -2328,7 +2328,7 @@
   // storage classes.
   if (!isa<CXXMethodDecl>(New) && !isa<CXXMethodDecl>(Old) &&
       New->getStorageClass() == SC_Static &&
-      Old->hasExternalLinkage() &&
+      isExternalLinkage(Old->getLinkage()) &&
       !New->getTemplateSpecializationInfo() &&
       !canRedefineFunction(Old, getLangOpts())) {
     if (getLangOpts().MicrosoftExt) {