Revert "Revert "ART: Mterp for arm64""

Looks like some of our assemblers disagree on valid arm64 assembly syntax
Force use of clang for art runtime.  In a subsequent CL, will use form
that both gcc and clang accept.

This reverts commit 43f3fb960bce978df699c8a68a972be2a0d0d221.

Change-Id: Ice83072171ab502c43d492e2238b446c4814ea67
diff --git a/runtime/Android.mk b/runtime/Android.mk
index 7bf6d21..288f95e 100644
--- a/runtime/Android.mk
+++ b/runtime/Android.mk
@@ -263,7 +263,8 @@
   arch/arm/fault_handler_arm.cc
 
 LIBART_TARGET_SRC_FILES_arm64 := \
-  interpreter/mterp/mterp_stub.cc \
+  interpreter/mterp/mterp.cc \
+  interpreter/mterp/out/mterp_arm64.S \
   arch/arm64/context_arm64.cc \
   arch/arm64/entrypoints_init_arm64.cc \
   arch/arm64/jni_entrypoints_arm64.S \
@@ -508,6 +509,7 @@
   ifeq ($$(art_target_or_host),target)
     $$(eval $$(call set-target-local-clang-vars))
     $$(eval $$(call set-target-local-cflags-vars,$(2)))
+    LOCAL_CLANG_arm64 := true
     LOCAL_CFLAGS_$(DEX2OAT_TARGET_ARCH) += -DART_DEFAULT_INSTRUCTION_SET_FEATURES="$(LIBART_TARGET_DEFAULT_INSTRUCTION_SET_FEATURES)"
     LOCAL_CFLAGS_$(2ND_DEX2OAT_TARGET_ARCH) += -DART_DEFAULT_INSTRUCTION_SET_FEATURES="$(2ND_LIBART_TARGET_DEFAULT_INSTRUCTION_SET_FEATURES)"
   else # host