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/execve.c

@@ -54,7 +54,7 @@ int execve(const char *prog, char *const argv[], char *const envp[]) {
   int rc;
   size_t i;
   if (!prog || !argv || !envp ||
-      (IsAsan() && (!__asan_is_valid(prog, 1) ||       //
+      (IsAsan() && (!__asan_is_valid_str(prog) ||      //
                     !__asan_is_valid_strlist(argv) ||  //
                     !__asan_is_valid_strlist(envp)))) {
     rc = efault();