Add clean step to introduce the newly added BUILD_EMULATOR.

Change-Id: I0de0625a12af0b98d6288df03024268326b909bf
diff --git a/CleanSpec.mk b/CleanSpec.mk
index df09e2a..922418a 100644
--- a/CleanSpec.mk
+++ b/CleanSpec.mk
@@ -130,6 +130,8 @@
 # Now we switched to build against Mac OS X SDK 10.6
 $(call add-clean-step, rm -rf $(OUT_DIR)/host/darwin-x86/obj)
 
+$(call add-clean-step, rm -f $(OUT_DIR)/versions_checked.mk)
+
 # ************************************************
 # NEWER CLEAN STEPS MUST BE AT THE END OF THE LIST
 # ************************************************