prefer (X ? 1 : -1) when converting from boolean (1,0) to int (1,-1)

prefer (X ? 1 : -1) when converting from boolean (1,0) to int (1,-1)

Formerly the style was sometimes 2*X - 1, because the C standard
was wrongly thought to disallow ?: in integral constant expressions.
* lib/inet_ntop.c (verify_int_size): Rewrite 2*X-7 (!) to 4<=X?1:-1.
* lib/signal.in.h (verify_NSIG_constraint): Rewrite 2*X-1 to X?1:-1.
* lib/spawn.in.h (verify_POSIX_SPAWN_USEVFORK_no_overlap): Likewise.
* lib/stdint.in.h (_verify_intmax_size): Likewise.
* lib/time.in.h (struct __time_t_must_be_integral): Rewrite
2 * ((time_t) 1 / 2 == 0) - 1 to (time_t) 1; this suffices to
verify that time_t cannot be floating.