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/unlinkat.c

@@ -40,7 +40,7 @@
  */
 int unlinkat(int dirfd, const char *path, int flags) {
   int rc;
-  if (IsAsan() && !__asan_is_valid(path, 1)) {
+  if (IsAsan() && !__asan_is_valid_str(path)) {
     rc = efault();
   } else if (_weaken(__zipos_notat) &&
              (rc = __zipos_notat(dirfd, path)) == -1) {