Sema: An extern declaration can't be a redeclaration of a parameter

In the following:
void f(int x) { extern int x; }

The second declaration of 'x' shouldn't be considered a redeclaration of
the parameter.

This is a different approach to r225780.

llvm-svn: 225875
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 7d1e28e..1bf57f6 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3285,12 +3285,12 @@
 
   // Check if extern is followed by non-extern and vice-versa.
   if (New->hasExternalStorage() &&
-      !Old->hasLinkage() && Old->isLocalVarDecl()) {
+      !Old->hasLinkage() && Old->isLocalVarDeclOrParm()) {
     Diag(New->getLocation(), diag::err_extern_non_extern) << New->getDeclName();
     Diag(OldLocation, PrevDiag);
     return New->setInvalidDecl();
   }
-  if (Old->hasLinkage() && New->isLocalVarDecl() &&
+  if (Old->hasLinkage() && New->isLocalVarDeclOrParm() &&
       !New->hasExternalStorage()) {
     Diag(New->getLocation(), diag::err_non_extern_extern) << New->getDeclName();
     Diag(OldLocation, PrevDiag);