IR: Add DeadGPRStoreElimination

This is based on the Flag Elimination pass, and is not optimal - but does eliminate quite a few dead stores.

External/FEXCore/Source/Interface/IR/PassManager.cpp

@@ -9,6 +9,7 @@ void PassManager::AddDefaultPasses(bool InlineConstants) {
   InsertPass(CreateConstProp(InlineConstants));
   ////// InsertPass(CreateDeadFlagCalculationEliminination());
   InsertPass(CreateDeadFlagStoreElimination());
+  InsertPass(CreateDeadGPRStoreElimination());
   InsertPass(CreateSyscallOptimization());
   InsertPass(CreatePassDeadCodeElimination());