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/clock_gettime.c

@@ -23,6 +23,7 @@
 #include "libc/dce.h"
 #include "libc/fmt/conv.h"
 #include "libc/intrin/asan.internal.h"
+#include "libc/intrin/describeflags.internal.h"
 #include "libc/nt/synchronization.h"
 #include "libc/sysv/errfuns.h"
 
@@ -70,7 +71,7 @@ noinstrument int clock_gettime(int clockid, struct timespec *ts) {
   }
   if (!__time_critical) {
     STRACE("clock_gettime(%d, [%s]) → %d% m", clockid,
-           __strace_timespec(buf, sizeof(buf), rc, ts), rc);
+           DescribeTimespec(buf, sizeof(buf), rc, ts), rc);
   }
   return rc;
 }