Code cleanup to avoid LLVM dependency when building with quick only.

Change-Id: I0985c227d775c72fd23975d4c9bf673ba32615c2
diff --git a/compiler/compiler_backend.h b/compiler/compiler_backend.h
index b20c125..01a69af 100644
--- a/compiler/compiler_backend.h
+++ b/compiler/compiler_backend.h
@@ -80,6 +80,9 @@
   }
 
   virtual bool IsPortable() const { return false; }
+  void SetBitcodeFileName(std::string const& filename) {
+    UNUSED(filename);
+  }
 
   virtual void InitCompilationUnit(CompilationUnit& cu) const = 0;