Fails to build on Fedora 21 and later

[pkit]

make[4]: Entering directory '/opt/zero/validator/native_client/src/shared/utils'
CC libutil_la-flags.lo
In file included from /usr/include/stdlib.h:24:0,
from flags.c:11:
/usr/include/features.h:148:3: error: #warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE" [-Werror=cpp]

warning "_BSD_SOURCE and _SVID_SOURCE are deprecated, use _DEFAULT_SOURCE"

^
cc1: all warnings being treated as errors

_DEFAULT_SOURCE definition should be added to all Makefile.am files
Or better use some automake macros.

https://groups.google.com/forum/#!topic/zerovm/YL0zPXat3XM