Make fixes and improvements

- Introduce __assert_disable global
- Improve strsignal() thread safety
- Make system call tracing thread safe
- Fix SO_RCVTIMEO / SO_SNDTIMEO on Windows
- Refactor DescribeFoo() functions into one place
- Fix fork() on Windows when TLS and MAP_STACK exist
- Round upwards in setsockopt(SO_RCVTIMEO) on Windows
- Disable futexes on OpenBSD which seem extremely broken
- Implement a better kludge for monotonic time on Windows

libc/intrin/strsignal.c

@@ -0,0 +1,67 @@
+/*-*- 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 2020 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/magnumstrs.internal.h"
+#include "libc/str/str.h"
+
+static char g_strsignal[12];
+
+/**
+ * Returns string describing signal code.
+ *
+ * This returns SIGZERO for 0 which is the empty value. Textual names
+ * should be available for signals 1 through 32. Signals in the range 33
+ * and 128 are returned as a `SIG%03d` string. Everything else is SIGWUT
+ *
+ * This function is thread safe when `sig` is a known signal magnum.
+ * Otherwise a pointer to static memory is returned which is unsafe.
+ *
+ * @param sig is signal number which should be in range 1 through 128
+ * @return pointer to static memory that mutates on subsequent calls
+ * @see sigaction()
+ * @threadsafe
+ */
+char *strsignal(int sig) {
+  char *p;
+  const char *s;
+  if (!sig) return "0";
+  if ((s = GetMagnumStr(kSignalNames, sig))) return s;
+  p = g_strsignal;
+  p[0] = 'S';
+  p[1] = 'I';
+  p[2] = 'G';
+  p[3] = 0;
+  if (!sig) {
+    p[3] = 'Z';
+    p[4] = 'E';
+    p[5] = 'R';
+    p[6] = 'O';
+    p[7] = 0;
+  } else if (1 <= sig && sig <= 128) {
+    p[3] = '0' + sig / 100;
+    p[4] = '0' + sig / 10 % 10;
+    p[5] = '0' + sig % 10;
+    p[6] = 0;
+  } else {
+    p[3] = 'W';
+    p[4] = 'U';
+    p[5] = 'T';
+    p[6] = 0;
+  }
+  return g_strsignal;
+}