PIE randomization

This patch is using mmap()'s randomization functionality in such a way that
it maps the main executable of (specially compiled/linked -pie/-fpie)
ET_DYN binaries onto a random address (in cases in which mmap() is allowed
to perform a randomization).

Origin of this patch is in exec-shield
(http://people.redhat.com/mingo/exec-shield/)

[jkosina@suse.cz: pie randomization: fix BAD_ADDR macro]
Signed-off-by: Jan Kratochvil <honza@jikos.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Roland McGrath <roland@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>