fix unsigned comparison bug in posix_spawn

read should never return anything but 0 or sizeof ec here, but if it
does, we want to treat any other return as "success". then the caller
will get back the pid and is responsible for waiting on it when it
immediately exits.

src/process/posix_spawn.c

@@ -152,7 +152,7 @@ int __posix_spawnx(pid_t *restrict res, const char *restrict path,
 	close(args.p[1]);
 
 	if (pid > 0) {
-		if (read(args.p[0], &ec, sizeof ec) < sizeof ec) ec = 0;
+		if (read(args.p[0], &ec, sizeof ec) != sizeof ec) ec = 0;
 		else waitpid(pid, &(int){0}, 0);
 	} else {
 		ec = -pid;