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

This reverts commit r225780, we can't compile line 181 in
sanitizer_platform_limits_posix.cc with this commit.

llvm-svn: 225781
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 82ffd4d..baa6822 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -3282,12 +3282,14 @@
   }
 
   // Check if extern is followed by non-extern and vice-versa.
-  if (New->hasGlobalStorage() && !Old->hasLinkage() && Old->hasLocalStorage()) {
+  if (New->hasExternalStorage() &&
+      !Old->hasLinkage() && Old->isLocalVarDecl()) {
     Diag(New->getLocation(), diag::err_extern_non_extern) << New->getDeclName();
     Diag(OldLocation, PrevDiag);
     return New->setInvalidDecl();
   }
-  if (Old->hasGlobalStorage() && !New->hasLinkage() && New->hasLocalStorage()) {
+  if (Old->hasLinkage() && New->isLocalVarDecl() &&
+      !New->hasExternalStorage()) {
     Diag(New->getLocation(), diag::err_non_extern_extern) << New->getDeclName();
     Diag(OldLocation, PrevDiag);
     return New->setInvalidDecl();