Added a patch approved in future llvm branches which stop argument promotion...

Added a patch approved in future llvm branches which stop argument promotion for variagic functions. This was required to stop auto promotion of arguments in __visc__ calls

llvm/lib/Transforms/IPO/ArgumentPromotion.cpp

@@ -125,6 +125,13 @@ CallGraphNode *ArgPromotion::PromoteArguments(CallGraphNode *CGN) {
   // Make sure that it is local to this module.
   if (!F || !F->hasLocalLinkage()) return 0;
 
+  // Don't promote arguments for variadic functions. Adding, removing, or
+  // changing non-pack parameters can change the classification of pack
+  // parameters. Frontends encode that classification at the call site in the
+  // IR, while in the callee the classification is determined dynamically
+  // on the number of registers consumed so far.
+  if (F->isVarArg()) return nullptr;
+
   // First check: see if there are any pointer arguments!  If not, quick exit.
   SmallVector<std::pair<Argument*, unsigned>, 16> PointerArgs;
   unsigned ArgNo = 0;