Disable Subzero IR generation for performance testing.

src/IceGlobalContext.h

Index: src/IceGlobalContext.h
diff --git a/src/IceGlobalContext.h b/src/IceGlobalContext.h
index b0fd0595e8f28125095e83e4ca19e8fede693724..bdc461e65867740b2a937ea22f2231166300f080 100644
--- a/src/IceGlobalContext.h
+++ b/src/IceGlobalContext.h
@@ -140,6 +140,10 @@ public:
 
   const ClFlags &getFlags() const { return Flags; }
 
+  bool isIRGenerationDisabled() const {
+    return ALLOW_DISABLE_IR_GEN ? getFlags().DisableIRGeneration : false;
+  }
+
   // Allocate data of type T using the global allocator.
   template <typename T> T *allocate() { return Allocator.Allocate<T>(); }