Fix perror fileno namespace (bug 17633).

Fix perror fileno namespace (bug 17633).

perror, an ISO C function, uses fileno, which is not an ISO C
function.  This patch makes it use __fileno instead.  (The nearby call
to fdopen is not a problem because that's #defined to _IO_new_fdopen.)

Tested for x86_64 (testsuite, and that installed stripped shared
libraries are unchanged by this patch).

	[BZ #17633]
	* stdio-common/perror.c (perror): Call __fileno instead of fileno.
	* conform/Makefile (test-xfail-ISO/stdio.h/linknamespace): Remove
	variable.
	(test-xfail-ISO99/stdio.h/linknamespace): Likewise.
	(test-xfail-ISO11/stdio.h/linknamespace): Likewise.