Fix proxygen OSS build

Summary: So far this is a speculative fix.. I am waiting to see the results from the Ubuntu machine, but I suspect this is the problem.

Reviewed By: bugok

Differential Revision: D2697600

fb-gh-sync-id: e33d452a52c5ace2b7401d6495621ce68a5076b5

folly/Makefile.am

@@ -280,6 +280,7 @@ nobase_follyinclude_HEADERS = \
 	test/function_benchmark/test_functions.h \
 	test/SynchronizedTestLib.h \
 	test/SynchronizedTestLib-inl.h \
+	test/TestUtils.h \
 	ThreadCachedArena.h \
 	ThreadCachedInt.h \
 	ThreadLocal.h \