Create os-syscall.h. The purpose of this file is to define anything
that's different among the BSDs, like system call numbers and
time_t. While there's a lot more different between the BSDs, this is at
least a start at capturing it.
Reviewed-by: Pierrick Bouvier <pierrick.bouvier@oss.qualcomm.com>
Signed-off-by: Warner Losh <imp@bsdimp.com>