First cut of PowerPC(64) support in LLDB.

Summary:
This adds preliminary support for PowerPC/PowerPC64, for FreeBSD.  There are
some issues still:

 * Breakpoints don't work well on powerpc64.
 * Shared libraries don't yet get loaded for a 32-bit process on powerpc64 host.
 * Backtraces don't work.  This is due to PowerPC ABI using a backchain pointer
   in memory, instead of a dedicated frame pointer register for the backchain.
 * Breakpoints on functions without debug info may not work correctly for 32-bit
   powerpc.

Reviewers: emaste, tfiala, jingham, clayborg

Reviewed By: clayborg

Subscribers: emaste, lldb-commits

Differential Revision: http://reviews.llvm.org/D5988

git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@220944 91177308-0d34-0410-b5e6-96231b3b80d8