Work around arm64 host prebuilt differences.

Change-Id: I345c994b06cc513f67270907f3877ad78dbadcc7
diff --git a/build/Android.common.mk b/build/Android.common.mk
index 07f5cd3..34b692f 100644
--- a/build/Android.common.mk
+++ b/build/Android.common.mk
@@ -91,9 +91,15 @@
 # Don't fail a dalvik minimal host build.
 -include $(LLVM_ROOT_PATH)/llvm.mk
 
-# Clang build support.
+# Clang build support. By default, host builds use clang for better warnings.
+# Target builds use GCC by default.
+# TODO: work out why arm64 target builds need GCC on the host.
 ART_TARGET_CLANG := false
-ART_HOST_CLANG := true
+ifneq ($(TARGET_ARCH),arm64)
+  ART_HOST_CLANG := true
+else
+  ART_HOST_CLANG := false
+endif
 
 # directory used for dalvik-cache on device
 ART_DALVIK_CACHE_DIR := /data/dalvik-cache