Include proper headers for sysctlbyname() on Mac OS

According to Xcode documentation[1], sysctlbyname is available on
Mac OS via the same includes as on FreeBSD/DragonFly.

[1] https://developer.apple.com/library/mac/documentation/Darwin/Reference/ManPages/man3/sysctlbyname.3.html

Signed-off-by: Erik de Castro Lopo <erikd@mega-nerd.com>
1 file changed