Save R9 when up-call.

Thanks to Ian who found this bug. This change can also fix a jni_internal_test
on device when we use -O2 instead of -O0.

Change-Id: I38ac829409aeacb120f5b3d239aedcd39ec32e63
diff --git a/src/compiler_llvm/runtime_support_llvm.cc b/src/compiler_llvm/runtime_support_llvm.cc
index 27541c3..2463bc5 100644
--- a/src/compiler_llvm/runtime_support_llvm.cc
+++ b/src/compiler_llvm/runtime_support_llvm.cc
@@ -61,8 +61,9 @@
 #endif
 }
 
-void art_set_current_thread_from_code(void* thread_object_addr) {
+void* art_set_current_thread_from_code(void* thread_object_addr) {
   // Nothing to be done.
+  return NULL;
 }
 
 void art_lock_object_from_code(Object* obj, Thread* thread) {