Merge from gnulib.

Merge from gnulib.

Include <stdio.h>, so that the caller
doesn't have to include <stdio.h> before us.
(clearerr_unlocked, feof_unlocked, ferror_unlocked,
fflush_unlocked, fgets_unlocked, fputc_unlocked, fputs_unlocked,
fread_unlocked, fwrite_unlocked, getc_unlocked, getchar_unlocked,
putc_unlocked, putchar_unlocked): Define to the unlocked counterpart
if not declared, so that we can use getpass.c code from libc without
rewriting it.
(flockfile, ftrylockfile, funlockfile): New macros.