Clarifying the wording of this diagnostic; it confused parameter and argument.

llvm-svn: 266644
diff --git a/clang/lib/Sema/SemaChecking.cpp b/clang/lib/Sema/SemaChecking.cpp
index b508693..b1e6b99 100644
--- a/clang/lib/Sema/SemaChecking.cpp
+++ b/clang/lib/Sema/SemaChecking.cpp
@@ -2723,7 +2723,7 @@
 
   if (!SecondArgIsLastNamedArgument)
     Diag(TheCall->getArg(1)->getLocStart(),
-         diag::warn_second_parameter_of_va_start_not_last_named_argument);
+         diag::warn_second_arg_of_va_start_not_last_named_param);
   else if (Type->isReferenceType()) {
     Diag(Arg->getLocStart(),
          diag::warn_va_start_of_reference_type_is_undefined);