Switch host builds to use Clang by default.

If LOCAL_CLANG is not set to false for a host module, clang will be used instead of gcc.

This also enables the integrated assembler by default for Darwin host builds.

bug 16172793

Change-Id: If7484c5dbcccce7d925bec97bff0a3e4c30e9434
diff --git a/CleanSpec.mk b/CleanSpec.mk
index 7b317e2..fef406c 100644
--- a/CleanSpec.mk
+++ b/CleanSpec.mk
@@ -244,6 +244,9 @@
 # dalvik.vm.image-dex2oat-Xms, and dalvik.vm.image-dex2oat-Xmx
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/root/default.prop)
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/recovery/root/default.prop)
+
+# Switch host builds to Clang by default
+$(call add-clean-step, rm -rf $(OUT_DIR)/host)
 # ************************************************
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST
 # ************************************************