PR20356: Fix all Sema warnings with mismatched ext_/warn_ versus
ExtWarn/Warnings. Mostly the name of the warning was changed to match the
semantics, but in the PR20356 cases, the warning was about valid code, so the
diagnostic was changed from ExtWarn to Warning instead.

llvm-svn: 213443
diff --git a/clang/lib/Sema/SemaDeclCXX.cpp b/clang/lib/Sema/SemaDeclCXX.cpp
index 3f9e63f..a0534ff 100644
--- a/clang/lib/Sema/SemaDeclCXX.cpp
+++ b/clang/lib/Sema/SemaDeclCXX.cpp
@@ -476,7 +476,7 @@
                                       OldParam->getUninstantiatedDefaultArg());
           else
             NewParam->setDefaultArg(OldParam->getInit());
-          DiagDefaultParamID = diag::warn_param_default_argument_redefinition;
+          DiagDefaultParamID = diag::ext_param_default_argument_redefinition;
           Invalid = false;
         }
       }