_DEFAULT_SOURCE replaces _BSD_SOURCE in glibc 2.19. However, the "Debian 7.11 2015-06-15 4GB SD LXDE" image referenced in the instructions has glibc 2.13. Keeping both lines in the Makefile should preserve compatibility for all versions of glibc.
53 is the reference issue, and this is the commit that introduced the issue.
(#57 was the original PR, but I accidentally dumped a lot more changes on it.)
_DEFAULT_SOURCEreplaces_BSD_SOURCEin glibc 2.19. However, the "Debian 7.11 2015-06-15 4GB SD LXDE" image referenced in the instructions has glibc 2.13. Keeping both lines in the Makefile should preserve compatibility for all versions of glibc.53 is the reference issue, and this is the commit that introduced the issue.
(#57 was the original PR, but I accidentally dumped a lot more changes on it.)