Made unknown builtin diagnostic remappable.

llvm-svn: 147774
diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index d80f22f7..54f953d 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -7253,7 +7253,7 @@
   // Extension in C99.  Legal in C90, but warn about it.
   unsigned diag_id;
   if (II.getName().startswith("__builtin_"))
-    diag_id = diag::err_builtin_unknown;
+    diag_id = diag::warn_builtin_unknown;
   else if (getLangOptions().C99)
     diag_id = diag::ext_implicit_function_decl;
   else