rm -rf in make clean

Summary: Without this I get bunch of questions when I run `make clean`

Test Plan: no more questions!

Reviewers: rven, yhchiang, meyering, anthony

Reviewed By: meyering, anthony

Subscribers: meyering, dhruba, leveldb

Differential Revision: https://reviews.facebook.net/D38145

Makefile

@@ -563,7 +563,7 @@ unity: unity.o
 clean:
 	rm -f $(BENCHMARKS) $(TOOLS) $(TESTS) $(LIBRARY) $(SHARED)
 	rm -rf $(CLEAN_FILES) ios-x86 ios-arm scan_build_report
-	find . -name "*.[oda]" -exec rm {} \;
+	find . -name "*.[oda]" -exec rm -f {} \;
 	find . -type f -regex ".*\.\(\(gcda\)\|\(gcno\)\)" -exec rm {} \;
 	rm -rf bzip2* snappy* zlib* lz4*