Add elision tunables

Add elision tunables

This patch adds several new tunables to control the behavior of
elision on supported platforms[1].   Since elision now depends
on tunables, we should always *compile* with elision enabled,
and leave the code disabled, but available for runtime
selection.  This gives us *much* better compile-time testing of
the existing code to avoid bit-rot[2].

Tested on ppc, ppc64, ppc64le, s390x and x86_64.

[1] This part of the patch was initially proposed by
Paul Murphy but was "staled" because the framework have changed
since the patch was originally proposed:

https://patchwork.sourceware.org/patch/10342/

[2] This part of the patch was inititally proposed as a RFC by
Carlos O'Donnell.  Make sense to me integrate this on the patch:

https://sourceware.org/ml/libc-alpha/2017-05/msg00335.html

	* elf/dl-tunables.list: Add elision parameters.
	* manual/tunables.texi: Add entries about elision tunable.
	* sysdeps/unix/sysv/linux/powerpc/elision-conf.c:
	Add callback functions to dynamically enable/disable elision.
	Add multiple callbacks functions to set elision parameters.
	Deleted __libc_enable_secure check.
	* sysdeps/unix/sysv/linux/s390/elision-conf.c: Likewise.
	* sysdeps/unix/sysv/linux/x86/elision-conf.c: Likewise.
	* configure: Regenerated.
	* configure.ac: Option enable_lock_elision was deleted.
	* config.h.in: ENABLE_LOCK_ELISION flag was deleted.
	* config.make.in: Remove references to enable_lock_elision.
	* manual/install.texi: Elision configure option was removed.
	* INSTALL: Regenerated to remove enable_lock_elision.
	* nptl/Makefile:
	Disable elision so it can verify error case for destroying a mutex.
	* sysdeps/powerpc/nptl/elide.h:
	Cleanup ENABLE_LOCK_ELISION check.
	Deleted macros for the case when ENABLE_LOCK_ELISION was not defined.
	* sysdeps/s390/configure: Regenerated.
	* sysdeps/s390/configure.ac: Remove references to enable_lock_elision..
	* nptl/tst-mutex8.c:
	Deleted all #ifndef ENABLE_LOCK_ELISION from the test.
	* sysdeps/powerpc/powerpc32/sysdep.h:
	Deleted all ENABLE_LOCK_ELISION checks.
	* sysdeps/powerpc/powerpc64/sysdep.h: Likewise.
	* sysdeps/powerpc/sysdep.h: Likewise.
	* sysdeps/s390/nptl/bits/pthreadtypes-arch.h: Likewise.
	* sysdeps/unix/sysv/linux/powerpc/force-elision.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/elision-conf.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/force-elision.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/lowlevellock.h: Likewise.
	* sysdeps/unix/sysv/linux/s390/Makefile: Remove references to
	enable-lock-elision.

Reviewed-by: Tulio Magno Quites Machado Filho <tuliom@linux.vnet.ibm.com>