Make terminal ui binaries work well everywhere

Here's some screenshots of an emulator tui program that was compiled on
Linux, then scp'd it to Windows, Mac, and FreeBSD.

https://justine.storage.googleapis.com/blinkenlights-cmdexe.png
https://justine.storage.googleapis.com/blinkenlights-imac.png
https://justine.storage.googleapis.com/blinkenlights-freebsd.png
https://justine.storage.googleapis.com/blinkenlights-lisp.png

How is this even possible that we have a nontrivial ui binary that just
works on Mac, Windows, Linux, and BSD? Surely a first ever achievement.

Fixed many bugs. Bootstrapped John McCarthy's metacircular evaluator on
bare metal in half the size of Altair BASIC (about 2.5kb) and ran it in
emulator for fun and profit.

libc/time/strftime.c

@@ -16,6 +16,7 @@
 │ IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED               │
 │ WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.          │
 ╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/assert.h"
 #include "libc/calls/calls.h"
 #include "libc/fmt/fmt.h"
 #include "libc/macros.h"
@@ -381,6 +382,7 @@ static char *strftime_timefmt(char *p, const char *pe, const char *format,
  */
 size_t strftime(char *s, size_t size, const char *f, const struct tm *t) {
   char *p;
+  assert(t);
   p = strftime_timefmt(s, s + size, f, t);
   if (p < s + size) {
     *p = '\0';