Cleanspec for libc++ migration.

This affects most native code in the tree, so the only real option is
to nuke out from orbit.

Change-Id: Ia3a794731e703c3ca02b55f6f7827d3425dca5cb

CleanSpec.mk

@@ -302,6 +302,9 @@ $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/build.prop)
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/system/app/*)
 $(call add-clean-step, rm -rf $(PRODUCT_OUT)/obj/APPS/*)
 
+# Move to libc++ as the default STL.
+$(call add-clean-step, rm -rf $(OUT_DIR))
+
 # ************************************************
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST
 # ************************************************