Make more threading improvements

- ASAN memory morgue is now lockless
- Make C11 atomics header more portable
- Rewrote pthread keys support to be lockless
- Simplify Python's unicode table unpacking code
- Make crash report write(2) closer to being atomic
- Make it possible to strace/ftrace a single thread
- ASAN now checks nul-terminated strings fast and properly
- Windows fork() now restores TLS memory of calling thread

libc/calls/execvpe.c

@@ -37,7 +37,7 @@
 int execvpe(const char *prog, char *const argv[], char *const *envp) {
   char *exe;
   char pathbuf[PATH_MAX];
-  if (IsAsan() && !__asan_is_valid(prog, 1)) return efault();
+  if (IsAsan() && !__asan_is_valid_str(prog)) return efault();
   if (!(exe = commandv(prog, pathbuf, sizeof(pathbuf)))) return -1;
   return execve(exe, argv, envp);
 }