[mod_cgi] FreeBSD 9.3/MacOSX does not have pipe2() (fixes #2765)
FreeBSD 9.3 has O_CLOEXEC, but does not have pipe2() until FreeBSD 10.
FreeBSD 10 also adds SOCK_CLOEXEC, so use that as indicator
https://wiki.freebsd.org/AtomicCloseOnExec
Note: FreeBSD 9.3 will soon reach its "extended" EOL date (31 Dec 2016),
so those using FreeBSD 9.3 should consider upgrading.
https://www.freebsd.org/security/security.html#sup
Mac OS X does not have pipe2(). User reported:
Undefined symbols for architecture x86_64:
"_pipe2", referenced from:
_mod_cgi_handle_subrequest in mod_cgi.o
x-ref:
"Undefined symbols _pipe2"
https://redmine.lighttpd.net/issues/2765