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/sys_gettid.greg.c

@@ -0,0 +1,64 @@
+/*-*- 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 2022 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/calls/syscall-sysv.internal.h"
+#include "libc/dce.h"
+#include "libc/nt/thread.h"
+#include "libc/nt/thunk/msabi.h"
+#include "libc/runtime/internal.h"
+
+__msabi extern typeof(GetCurrentThreadId) *const __imp_GetCurrentThreadId;
+
+privileged int sys_gettid(void) {
+  int tid;
+  int64_t wut;
+  if (IsWindows()) {
+    tid = __imp_GetCurrentThreadId();
+  } else if (IsLinux()) {
+    asm("syscall"
+        : "=a"(tid)  // man says always succeeds
+        : "0"(186)   // __NR_gettid
+        : "rcx", "r11", "memory");
+  } else if (IsXnu()) {
+    asm("syscall"              // xnu/osfmk/kern/ipc_tt.c
+        : "=a"(tid)            // assume success
+        : "0"(0x1000000 | 27)  // Mach thread_self_trap()
+        : "rcx", "r11", "memory", "cc");
+  } else if (IsOpenbsd()) {
+    asm("syscall"
+        : "=a"(tid)  // man says always succeeds
+        : "0"(299)   // getthrid()
+        : "rcx", "r11", "memory", "cc");
+  } else if (IsNetbsd()) {
+    asm("syscall"
+        : "=a"(tid)  // man says always succeeds
+        : "0"(311)   // _lwp_self()
+        : "rcx", "rdx", "r11", "memory", "cc");
+  } else if (IsFreebsd()) {
+    asm("syscall"
+        : "=a"(tid),  // only fails w/ EFAULT, which isn't possible
+          "=m"(wut)   // must be 64-bit
+        : "0"(432),   // thr_self()
+          "D"(&wut)   // but not actually 64-bit
+        : "rcx", "r11", "memory", "cc");
+    tid = wut;
+  } else {
+    tid = __pid;
+  }
+  return tid;
+}