ARM: Allow auto-detection of linker relro feature

Set values for libc_commonpagesize and libc_relro_required for the
ARM port to enable relro by default and suppress a warning at
configure time.

ChangeLog:

2014-05-09  Will Newton  <will.newton@linaro.org>

	* sysdeps/arm/preconfigure.ac: Set libc_commonpagesize
	and libc_relro_required for ARM.
	* sysdeps/arm/preconfigure: Regenerate.