os: add support for signal handling on JS backend (#12818)

vlib/os/signal.c.v

@@ -2,48 +2,6 @@ module os
 
 #include <signal.h>
 
-// os.Signal - enumerate possible POSIX signals and
-// their integer codes.
-// NB: the integer codes are given here explicitly,
-// to make it easier to lookup, without needing to
-// consult man pages / signal.h .
-
-pub enum Signal {
-	hup = 1
-	int = 2
-	quit = 3
-	ill = 4
-	trap = 5
-	abrt = 6
-	bus = 7
-	fpe = 8
-	kill = 9
-	usr1 = 10
-	segv = 11
-	usr2 = 12
-	pipe = 13
-	alrm = 14
-	term = 15
-	stkflt = 16
-	chld = 17
-	cont = 18
-	stop = 19
-	tstp = 20
-	ttin = 21
-	ttou = 22
-	urg = 23
-	xcpu = 24
-	xfsz = 25
-	vtalrm = 26
-	prof = 27
-	winch = 28
-	poll = 29
-	pwr = 30
-	sys = 31
-}
-
-type SignalHandler = fn (Signal)
-
 fn C.signal(signal int, handlercb SignalHandler) voidptr
 
 // signal will assign `handler` callback to be called when `signum` signal is received.