Fix clean-oat-host.

Only clean normal files, avoiding ART module folders
    com.android.art
that end with the same ".art" suffix as image files.

Test: m && m clean-oat-host
Change-Id: I3ee334cc626fa090a639938c4576f781f458d1fa
diff --git a/Android.mk b/Android.mk
index a3bdb9e..36e5b90 100644
--- a/Android.mk
+++ b/Android.mk
@@ -30,7 +30,7 @@
 
 .PHONY: clean-oat-host
 clean-oat-host:
-	find $(OUT_DIR) -name "*.oat" -o -name "*.odex" -o -name "*.art" -o -name '*.vdex' | xargs rm -f
+	find $(OUT_DIR) '(' -name '*.oat' -o -name '*.odex' -o -name '*.art' -o -name '*.vdex' ')' -a -type f | xargs rm -f
 	rm -rf $(TMPDIR)/*/test-*/dalvik-cache/*
 	rm -rf $(TMPDIR)/android-data/dalvik-cache/*