Use kern.proc.auxv to get the aux data

Summary:
Instead of using a homegrown solution to get the auxv from a process, instead
use the OS-provided sysctl to get the needed data.  This allows the same code to
be used for both 32-bit and 64-bit processes on a 64-bit host.

Reviewers: emaste

Reviewed By: emaste

Subscribers: emaste, lldb-commits

Differential Revision: http://reviews.llvm.org/D6071