Fix LLVM build. Otherwise, function not used warning.

Note that we use -Werror.

Change-Id: I14c2d1d040d392cf5b2866298dc9c62a216f329b
diff --git a/src/native/dalvik_system_VMRuntime.cc b/src/native/dalvik_system_VMRuntime.cc
index fe52ae4..caac283 100644
--- a/src/native/dalvik_system_VMRuntime.cc
+++ b/src/native/dalvik_system_VMRuntime.cc
@@ -124,9 +124,11 @@
   return env->NewStringUTF(Runtime::Current()->GetVersion());
 }
 
+#if !defined(ART_USE_LLVM_COMPILER)
 static void DisableCheckJniCallback(Thread* t, void*) {
   t->GetJniEnv()->SetCheckJniEnabled(false);
 }
+#endif
 
 static void VMRuntime_setTargetSdkVersion(JNIEnv*, jobject, jint targetSdkVersion) {
   // This is the target SDK version of the app we're about to run.