build: build as POSIX 2008 source
build: build as POSIX 2008 source

Some of the functions we want to use (e.g., openat) are part of the 2008
version.  On some systems (notably FreeBSD) the prototypes and defines are
not visible unless we declare our desire to use the 2008 version of the
standard.

Signed-off-by: Josef 'Jeff' Sipek <a620f141433c70aa9e43778305a6c68cbfadfb25@josefsipek.net>

jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc,jeffpc/libjeffpc