Make POSIX threads improvements

- Ensure SIGTHR isn't blocked in newly created threads
- Use TIB rather than thread_local for thread atexits
- Make POSIX thread keys atomic within thread
- Don't bother logging prctl() to --strace
- Log thread destructor names to --strace

libc/intrin/describeprctloperation.c

@@ -1,39 +0,0 @@
-/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
-│ vi: set et 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/intrin/describeflags.internal.h"
-#include "libc/sysv/consts/pr.h"
-
-const char *DescribePrctlOperation(int x) {
-  switch (x) {
-    case PR_GET_NAME:
-      return "PR_GET_NAME";
-    case PR_SET_NO_NEW_PRIVS:
-      return "PR_SET_NO_NEW_PRIVS";
-    case PR_SET_SECCOMP:
-      return "PR_SET_SECCOMP";
-    case PR_GET_SECCOMP:
-      return "PR_GET_SECCOMP";
-    case PR_CAPBSET_READ:
-      return "PR_CAPBSET_READ";
-    case PR_CAPBSET_DROP:
-      return "PR_CAPBSET_DROP";
-    default:
-      return "PRCTL_???";
-  }
-}