Remove arm64 clang build warning

Now we have enabled arm64 clang.
This change remvoed arm64 clang build warning and cleaned the
arm64 unknow c flags.

Change-Id: Ia583a78c6d364e603ff09df423aa34a6e03d0b9b

core/clang/TARGET_arm64.mk

@@ -50,5 +50,4 @@ CLANG_TARGET_GLOBAL_LDFLAGS := \
   $(call convert-to-clang-flags,$(TARGET_GLOBAL_LDFLAGS)) \
   $(CLANG_CONFIG_arm64_TARGET_EXTRA_LDFLAGS)
 
-$(warning Incorrect arm64 RS_TRIPLE, fix me!)
 RS_TRIPLE := aarch64-linux-android

core/clang/arm64.mk

@@ -1,7 +1,5 @@
 # Clang flags for arm64 arch, target or host.
 
-$(warning Untested arm64 clang flags, fix me!)
-
 CLANG_CONFIG_arm64_EXTRA_ASFLAGS :=
 
 CLANG_CONFIG_arm64_EXTRA_CFLAGS := \
@@ -12,18 +10,14 @@ CLANG_CONFIG_arm64_EXTRA_LDFLAGS :=
 # Include common unknown flags
 CLANG_CONFIG_arm64_UNKNOWN_CFLAGS := \
   $(CLANG_CONFIG_UNKNOWN_CFLAGS) \
-  -mthumb-interwork \
   -fgcse-after-reload \
   -frerun-cse-after-loop \
   -frename-registers \
-  -fno-builtin-sin \
   -fno-strict-volatile-bitfields \
   -fno-align-jumps \
   -Wa,--noexecstack
 
+# We don't have any arm64 flags to substitute yet.
 define subst-clang-incompatible-arm64-flags
-  $(subst -march=armv5te,-march=armv5t,\
-  $(subst -march=armv5e,-march=armv5,\
-  $(subst -mcpu=cortex-a15,-march=armv7-a,\
-  $(1))))
+  $(1)
 endef

core/combo/TARGET_linux-arm64.mk

@@ -47,9 +47,6 @@ ifeq ($(strip $(wildcard $(TARGET_ARCH_SPECIFIC_MAKEFILE))),)
 $(error Unknown ARM architecture version: $(TARGET_ARCH_VARIANT))
 endif
 
-# TODO: Enable Clang when aarch64 prebuilt is added
-# WITHOUT_TARGET_CLANG := true
-
 include $(TARGET_ARCH_SPECIFIC_MAKEFILE)
 
 # You can set TARGET_TOOLS_PREFIX to get gcc from somewhere else