Fix warnings

This change fixes Cosmopolitan so it has fewer opinions about compiler
warnings. The whole repository had to be cleaned up to be buildable in
-Werror -Wall mode. This lets us benefit from things like strict const
checking. Some actual bugs might have been caught too.

libc/calls/clock_gettime-mono.c

@@ -37,7 +37,6 @@ static void sys_clock_gettime_mono_init(void) {
 int sys_clock_gettime_mono(struct timespec *time) {
   uint64_t nanos;
   uint64_t cycles;
-  struct timespec res;
   if (X86_HAVE(INVTSC)) {
     cosmo_once(&g_mono.once, sys_clock_gettime_mono_init);
     cycles = rdtsc() - g_mono.base_tick;