Make improvements

- Implement openpty()
- Add `--assimilate` flag to APE bootloader
- Restore Linux vDSO clock_gettime() support
- Use `$(APE_NO_MODIFY_SELF)` on more programs

libc/calls/clock_gettime-nt.c

@@ -27,6 +27,7 @@ textwindows int sys_clock_gettime_nt(int clockid, struct timespec *ts) {
   struct timespec res;
   struct NtFileTime ft;
   static struct timespec mono;
+  if (!ts) return efault();
   if (clockid == CLOCK_REALTIME) {
     GetSystemTimeAsFileTime(&ft);
     *ts = FileTimeToTimeSpec(ft);