Don't get confused if a extern "C" builtin function is redeclared without
the extern "C".

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@171260 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/AST/Decl.cpp b/lib/AST/Decl.cpp
index 92b1e4a..2d34e4c 100644
--- a/lib/AST/Decl.cpp
+++ b/lib/AST/Decl.cpp
@@ -2440,7 +2440,7 @@
     return Builtin::BIstrlen;
 
   default:
-    if (isExternC()) {
+    if (hasCLanguageLinkage()) {
       if (FnInfo->isStr("memset"))
         return Builtin::BImemset;
       else if (FnInfo->isStr("memcpy"))