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/intrin/formatint64.c

@@ -0,0 +1,55 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2021 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/fmt/itoa.h"
+
+/**
+ * Converts unsigned 64-bit integer to string.
+ *
+ * @param p needs at least 21 bytes
+ * @return pointer to nul byte
+ */
+dontinline char *FormatUint64(char p[static 21], uint64_t x) {
+  char t;
+  size_t i, a, b;
+  i = 0;
+  do {
+    p[i++] = x % 10 + '0';
+    x = x / 10;
+  } while (x > 0);
+  p[i] = '\0';
+  if (i) {
+    for (a = 0, b = i - 1; a < b; ++a, --b) {
+      t = p[a];
+      p[a] = p[b];
+      p[b] = t;
+    }
+  }
+  return p + i;
+}
+
+/**
+ * Converts signed 64-bit integer to string.
+ *
+ * @param p needs at least 21 bytes
+ * @return pointer to nul byte
+ */
+char *FormatInt64(char p[static 21], int64_t x) {
+  if (x < 0) *p++ = '-', x = -(uint64_t)x;
+  return FormatUint64(p, x);
+}