The flag -fsanitize=default is used if it is available (GCC 4.9 or later) to detect undefined behavior. Unfortunately, the implementation in GCC seems to have some bugs with GCC 4.9.2, see https://bugzilla.redhat.com/show_bug.cgi?id=1166173 for more details.

Since the supported compiler at the moment is GCC 4.8.2, I suggest that we remove the flag and when we upgrade the supported compiler to GCC 4.9.X, then we can reevaluate whether we should use -fsanitize=default or not.