[PATCH] Fix recent <bits/stdio-lock.h> breakage

[Roland McGrath]

That seems kind of ugly to me, especially copying the type definitions.

Perhaps the simplest thing to do is treat _IO_MTSAFE_IO like _LIBC in
libc-lock.h, so it defines all the real types when building libio.

That is sort of unkosher, but using libio's _IO_MTSAFE_IO like this in
libc seems morally equivalent to libio's unkosher use of <bits/*.h> headers.