Remove relro configure test.

Remove relro configure test.

This patch removes the configure test for working -z relro.

The use of -z relro in Makeconfig became unconditional with

commit 2e6ab1df44c412bb9d30b26a4d8a679150a7e375
Author: Ulrich Drepper <drepper@redhat.com>
Date:   Sat Oct 28 06:44:04 2006 +0000

    Remove conditional code which now is unnecessary.

(commit reference from git://repo.or.cz/glibc/history), so since then
the configure test has not controlled anything about how glibc is
built - simply about whether configure succeeds and allows a build to
be attempted.  The test for whether the option did something useful
(as opposed to whether it exists - which we can certainly just assume
by now) was originally added in
<https://sourceware.org/ml/libc-hacker/2004-09/msg00069.html> to
disable the option in a case when it did nothing useful on ia64 (as a
result of something deliberate in the linker on ia64).  Since 2006
that disabling has been of no effect, and given that the current test
does not set libc_relro_required for ia64, it does nothing whatever
useful for the original motivating case.  Also at around the same time
in 2006 the test was made to give an error for missing or broken -z
relro support on various architectures.

So effectively all the test does now is verify that, on certain
architectures, the linker has not been changed deliberately to make
the option ineffective.  I see no apparent reason why such a change
should be expected, or why the build should be stopped if it were to
be made (any more than we disallow build on ia64); I think we can
trust binutils patch review to point out the consequences of any
change to COMMONPAGESIZE setting.  The only thing that might now make
sense would be disabling the -z relro use on an architecture-specific
basis if there were an architecture-specific reason to consider that
to make sense; it would be for the ia64 maintainer to decide if that
makes sense for ia64 at present, but I think that could be done
through sysdeps Makefiles - no special configure tests needed.

Tested for x86_64 that this patch makes no change to the installed
shared libraries.

Together with
<https://sourceware.org/ml/libc-alpha/2014-06/msg00788.html> (pending
review) this substantially eliminates architecture-specific cases from
architecture-independent configure.ac files.  There remains an i386
case in sysdeps/mach/hurd/configure.ac that should properly move to
the i386 subdirectory.  (There are also OS-specific cases outside
OS-specific directories; in principle I think should should also
move.)

	* configure.ac (libc_commonpagesize): Remove variable.
	(libc_relro_required): Likewise.
	(libc_cv_z_relro): Remove configure test.
	* configure: Regenerated.
	* sysdeps/aarch64/preconfigure (libc_commonpagesize): Do not set
	variable.
	(libc_relro_required): Likewise.
	* sysdeps/alpha/preconfigure (libc_commonpagesize): Likewise.
	(libc_relro_required): Likewise.
	* sysdeps/arm/preconfigure.ac (libc_commonpagesize): Likewise.
	(libc_relro_required): Likewise.
	* sysdeps/arm/preconfigure: Regenerated.
	* sysdeps/ia64/preconfigure: Remove file.
	* sysdeps/tile/preconfigure (libc_commonpagesize): Do not set
	variable.
	(libc_relro_required): Likewise.