GCC compatibility: gcc allows applying va_args to const 
va_lists for some reason.  This fixes rdar://6726818


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@68434 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Sema/SemaExpr.cpp b/lib/Sema/SemaExpr.cpp
index 55eaaa4..a43c2c3 100644
--- a/lib/Sema/SemaExpr.cpp
+++ b/lib/Sema/SemaExpr.cpp
@@ -4724,7 +4724,10 @@
   Expr *E = static_cast<Expr*>(expr.get());
   UsualUnaryConversions(E);
 
-  if (CheckAssignmentConstraints(VaListType, E->getType()) != Compatible)
+  AssignConvertType ConvResult = 
+    CheckAssignmentConstraints(VaListType, E->getType());
+  if (ConvResult != Compatible &&
+      ConvResult != CompatiblePointerDiscardsQualifiers)
     return ExprError(Diag(E->getLocStart(),
                          diag::err_first_argument_to_va_arg_not_of_type_va_list)
       << E->getType() << E->getSourceRange());