Preserve bound registers for pointer pass/return

Preserve bound registers for pointer pass/return

We need to save/restore bound registers and add a BND prefix before
branches in _dl_runtime_profile so that bound registers for pointer
pass and return are preserved when LD_AUDIT is used.

	[BZ #18134]
	* sysdeps/i386/configure.ac: Set HAVE_MPX_SUPPORT.
	* sysdeps/i386/configure: Regenerated.
	* sysdeps/i386/dl-trampoline.S (PRESERVE_BND_REGS_PREFIX): New.
	(_dl_runtime_profile): Save and restore Intel MPX return bound
	registers when calling _dl_call_pltexit.  Add
	PRESERVE_BND_REGS_PREFIX before return.
	* sysdeps/i386/link-defines.sym (LRV_BND0_OFFSET): New.
	(LRV_BND1_OFFSET): Likewise.
	* sysdeps/x86/bits/link.h (La_i86_retval): Add lrv_bnd0 and
	lrv_bnd1.
	* sysdeps/x86_64/dl-trampoline.S (_dl_runtime_profile): Fix
	typo in bndmov encoding.
	* sysdeps/x86_64/dl-trampoline.h: Properly save and restore
	Intel MPX bound registers.  Add PRESERVE_BND_REGS_PREFIX before
	branch instructions to preserve bounds.