spawn

Do not require C99 mode for older GCC (#62) Signed-off-by: Jonah Beckford <71855677+jonahbeckford@users.noreply.github.com> Co-authored-by: Jonah Beckford <9566106-jonahbeckford@users.noreply.gitlab.com>

Haiku Rationale : POSIX is clear that signal ordering is not guaranteed. On Haiku, SIGKILL is sent at higher priority than SIGUSR1 so it is signaled before. Here the goal is just to test the masking, so i change for SIGUSR2 at same level. Though i am aware there should be a cleaner way to test signal masking, this change gets the signals to be delivered in same order. This solved the FAILED test on Haiku. Signed-off-by: Sylvain78 <sylvain_kerjean@hotmail.com>