Defining only _BSD_SOURCE is deprecated with version 2.20 of
glibc. It has been replaced by _DEFAULT_SOURCE. The manpage says
that code which wants to work in the same way on both old and new
versions of glibc should simply define both symbols.

Also move the definition up in fix_size as those feature flags
should be defined before including any standard headers.

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>