Subzero. Adds a pass for target-specific helper call generation.

src/IceTargetLoweringX86Base.h

Index: src/IceTargetLoweringX86Base.h
diff --git a/src/IceTargetLoweringX86Base.h b/src/IceTargetLoweringX86Base.h
index 90bbed27ac8ecb6f6ced71101be76d35e0cf7754..3127151c3aa2651a9695f531b53dfb82ef207f49 100644
--- a/src/IceTargetLoweringX86Base.h
+++ b/src/IceTargetLoweringX86Base.h
@@ -182,6 +182,7 @@ protected:
   void lowerOther(const Inst *Instr) override;
   void lowerRMW(const typename Traits::Insts::FakeRMW *RMW);
   void prelowerPhis() override;
+  void genTargetHelperCallFor(Inst *Instr) override { (void)Instr; }
   void doAddressOptLoad() override;
   void doAddressOptStore() override;
   void doMockBoundsCheck(Operand *Opnd) override;