Make improvements

- Get threads working on NetBSD
- Get threads working on OpenBSD
- Fix Emacs config for Emacs v28
- Improve --strace logging of sigset_t
- Improve --strace logging of struct stat
- Improve memory safety of DescribeThing functions
- Refactor auto stack allocation into LIBC_RUNTIME
- Introduce shell.com example which works on Windows
- Refactor __strace_thing into DescribeThing functions
- Document the CHECK macros and improve them in NDEBUG mode
- Rewrite MAP_STACK so it uses FreeBSD behavior across platforms
- Deprecate and discourage the use of MAP_GROWSDOWN (it's weird)

libc/calls/poll.c

@@ -84,20 +84,22 @@ int poll(struct pollfd *fds, size_t nfds, int timeout_ms) {
 
 #if defined(SYSDEBUG) && _POLLTRACE
   if (__strace > 0) {
-    if (rc == -1 && errno == EFAULT) {
-      STRACE("poll(%p, %'lu, %'d) → %d% lm", fds, nfds, timeout_ms, rc);
+    kprintf(STRACE_PROLOGUE "poll(");
+    if ((!IsAsan() && kisdangerous(fds)) ||
+        (IsAsan() && !__asan_is_valid(fds, nfds * sizeof(struct pollfd)))) {
+      kprintf("%p", fds);
     } else {
       char flagbuf[2][64];
-      kprintf(STRACE_PROLOGUE "poll({");
+      kprintf("[{");
       for (i = 0; i < MIN(5, nfds); ++i) {
         kprintf(
             "%s{%d, %s, %s}", i ? ", " : "", fds[i].fd,
             DescribePollFlags(flagbuf[0], sizeof(flagbuf[0]), fds[i].events),
             DescribePollFlags(flagbuf[1], sizeof(flagbuf[1]), fds[i].revents));
       }
-      kprintf("%s}, %'zu, %'d) → %d% lm\n", i == 5 ? "..." : "", nfds,
-              timeout_ms, rc);
+      kprintf("%s}]", i == 5 ? "..." : "");
     }
+    kprintf(", %'zu, %'d) → %d% lm\n", nfds, timeout_ms, rc);
   }
 #endif