Code review comment for lp://staging/~albaguirre/mir/possibly-fix-yakkety-build-failure

LGTM.

from “man feature_test_macros”
_BSD_SOURCE:
…
          Since glibc 2.20, this macro is deprecated. It now has the same effect as defining _DEFAULT_SOURCE, but generates a compile-time warning (unless _DEFAULT_SOURCE is also defined). Use
          _DEFAULT_SOURCE instead. To allow code that requires _BSD_SOURCE in glibc 2.19 and earlier and _DEFAULT_SOURCE in glibc 2.20 and later to compile without warnings, define both _BSD_SOURCE and
          _DEFAULT_SOURCE.