Fix bugs and update the LIT test for linear scan RA

So that linear scan RA driver can be built to do regression test

Author: bcheng0127

visa/LinearScanRA.cpp

@@ -1547,8 +1547,7 @@ void LinearScanRA::calculateCurrentBBLiveIntervals(
         liveIntervals.push_back(stackCallRetLR);
         stackCallRetLR->setPushed(true);
       }
-      if (arg && argSize > 0 && arg->getRegVar()) {
-        vASSERT(stackCallArgLR);
+      if (stackCallArgLR && arg && argSize > 0 && arg->getRegVar()) {
         stackCallArgLR->setLastRef(
             curInst, curInst->getLexicalId() * 2 -
                          1); // Minus one so that arguments will not be spilled