Access out of scope fix in OCLToSPIRVBase::transBuiltin (#2262)

OldRetTy pointer was passed to lambda by reference. This means that
in lambda it's real C-like type was Value ** pointing to the stack
within of the transBuiltin stack frame. Logic of lambda is executed in
doConversion function executed in destructor of BuiltinCallMutator.
The stack frame is unaccessible during the destructor call and
it worked only as undfined behaviour.

Original commit:
KhronosGroup/SPIRV-LLVM-Translator@85a10e2

Author: bwlodarcz

llvm-spirv/lib/SPIRV/OCLToSPIRV.cpp

@@ -912,16 +912,16 @@ void OCLToSPIRVBase::transBuiltin(CallInst *CI, OCLBuiltinTransInfo &Info) {
     Info.UniqName = getSPIRVFuncName(BVKind);
   } else
     return;
-  auto Mutator = mutateCallInst(CI, Info.UniqName + Info.Postfix);
+  BuiltinCallMutator Mutator = mutateCallInst(CI, Info.UniqName + Info.Postfix);
   Info.PostProc(Mutator);
   if (Info.RetTy) {
     Type *OldRetTy = CI->getType();
     Mutator.changeReturnType(
-        Info.RetTy, [&](IRBuilder<> &Builder, CallInst *NewCI) {
-          if (Info.RetTy->isIntegerTy() && OldRetTy->isIntegerTy())
+        Info.RetTy, [OldRetTy, &Info](IRBuilder<> &Builder, CallInst *NewCI) {
+          if (Info.RetTy->isIntegerTy() && OldRetTy->isIntegerTy()) {
             return Builder.CreateIntCast(NewCI, OldRetTy, Info.IsRetSigned);
-          else
-            return Builder.CreatePointerBitCastOrAddrSpaceCast(NewCI, OldRetTy);
+          }
+          return Builder.CreatePointerBitCastOrAddrSpaceCast(NewCI, OldRetTy);
         });
   }
 }