liblockdep: Support using LD_PRELOAD

This allows lockdep to be used without being compiled in the
original program.

Usage is quite simple:

	LD_PRELOAD=/path/to/liblockdep.so /path/to/my/program

And magically, you'll have lockdep checking in your program!

Signed-off-by: Sasha Levin <sasha.levin@oracle.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: torvalds@linux-foundation.org
Link: http://lkml.kernel.org/r/1371163284-6346-8-git-send-email-sasha.levin@oracle.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>