[TableGen] Workaround for VS 2015 Update 3 RelWithDebInfo build

[andrewng]

Summary

Commit r315884 introduced a build issue for VS 2015 Update 3 in the
RelWithDebInfo build. The issue is a fatal internal error in the CL
compiler caused by the following line of code in the function
OperandMatcher::addTypeCheckPredicate:

addPredicate<LLTOperandMatcher>(*OpTyOrNone);

The workaround is to replace *OpTyOrNone with a local variable of type
const LLTCodeGen & referring to *OpTyOrNone.

[andrewng]

Workaround no longer required. This issue is also fixed by commit r315932.

utils/TableGen/GlobalISelEmitter.cpp

Error addTypeCheckPredicate(const TypeSetByHwMode &VTy,
 
     auto OpTyOrNone = MVTToLLT(VTy.getMachineValueType().SimpleTy);
     if (!OpTyOrNone)
       return failedImport("unsupported type");
 
     if (OperandIsAPointer)
       addPredicate<PointerToAnyOperandMatcher>(
           OpTyOrNone->get().getSizeInBits());
-    else
-      addPredicate<LLTOperandMatcher>(*OpTyOrNone);
+    else {
+      // The following local variable is not needed but is a workaround for a VS
+      // 2015 Update 3 CL internal error when building RelWithDebInfo.
+      const LLTCodeGen &OpTy = *OpTyOrNone;
+      addPredicate<LLTOperandMatcher>(OpTy);
+    }
     return Error::success();
   }
 
   /// Emit MatchTable opcodes to capture instructions into the MIs table.
   void emitCaptureOpcodes(MatchTable &Table, RuleMatcher &Rule,
                           unsigned InsnVarID) const {
     for (const auto &Predicate : predicates())
       Predicate->emitCaptureOpcodes(Table, Rule, InsnVarID, OpIdx);