S/390: Port of lock elision to System/z

Added support for TX lock elision of pthread mutexes on s390 and
s390x.  This may improve lock scaling of existing programs on TX
capable systems.  The lock elision code is only built with
--enable-lock-elision=yes and then requires a GCC version supporting
the TX builtins.  With lock elision default mutexes are elided via
__builtin_tbegin, if the cpu supports transactions. By default lock
elision is not enabled and the elision code is not built.
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.