Make improvements

- Improved async signal safety of read() particularly for longjmp()
- Started adding cancel cleanup handlers for locks / etc on Windows
- Make /dev/tty work better particularly for uses like `foo | less`
- Eagerly read console input into a linked list, so poll can signal
- Fix some libc definitional bugs, which configure scripts detected

libc/stdio/dirstream.c

@@ -677,3 +677,4 @@ void seekdir(DIR *dir, long tell) {
 }
 
 __weak_reference(readdir, readdir64);
+__weak_reference(readdir_r, readdir_r64);