Improve Windows Console I/O

- Blocking read operations on the Windows Console can now EINTR
- Blocking read operations on Windows pipes now EINTR more reliably
- setitimer() will no longer be inherited across fork() on Windows
- It's now possible to use ECHO when the console is in raw mode
- The ECHOCTL flag now works correctly on the Windows Console
- The ICRNL flag now works correctly on the Windows Console
- pread() and pwrite() will now raise ESPIPE on Windows
- Opening /dev/tty on Windows is improved (untested)
- Overlapped I/O is now implemented in a better way

libc/stdio/fgets.c

@@ -26,6 +26,9 @@
  * exceeding size. The line ending marker is included and may be removed
  * using _chomp().
  *
+ * When reading from the console on Windows in `ICANON` mode, the
+ * returned line will end with `\r\n` rather than `\n`.
+ *
  * @param s is output buffer
  * @param size is capacity of s
  * @param f is non-null file object stream pointer