Make improvements

- More timspec_*() and timeval_*() APIs have been introduced.
- The copyfd() function is now simplified thanks to POSIX rules.
- More Cosmo-specific APIs have been moved behind the COSMO define.
- The setitimer() polyfill for Windows NT is now much higher quality.
- Fixed build error for MODE=aarch64 due to -mstringop-strategy=loop.
- This change introduces `make MODE=nox87 toolchain` which makes it
  possible to build programs using your cosmocc toolchain that don't
  have legacy fpu instructions. This is useful, for example, if you
  want to have a ~22kb tinier blink virtual machine.

third_party/nsync/futex.c

@@ -202,11 +202,7 @@ static struct timespec *nsync_futex_timeout_ (struct timespec *memory,
 		return memory;
 	} else {
 		now = timespec_real ();
-		if (timespec_cmp (now, *abstime) > 0) {
-			*memory = (struct timespec){0};
-		} else {
-			*memory = timespec_sub (*abstime, now);
-		}
+		*memory = timespec_subz (*abstime, now);
 		return memory;
 	}
 }