Add MemoryRegionInfo to SB API

Summary:
This adds new SB API calls and classes to allow a user of the SB API to obtain a full list of memory regions accessible within the process. Adding this to the API makes it possible use the API for tasks like scanning memory for blocks allocated with a header and footer to track down memory leaks, otherwise just inspecting every address is impractical especially for 64 bit processes.

These changes only add the API itself and a base implementation of GetMemoryRegions() to lldb_private::Process::GetMemoryRegions.
I will submit separate patches to fill in lldb_private::Process::GetMemoryRegionInfoList and GetMemoryRegionInfo for individual platforms.

The original discussion about this is here:
http://lists.llvm.org/pipermail/lldb-dev/2016-May/010203.html

Reviewers: clayborg

Subscribers: lldb-commits

Differential Revision: http://reviews.llvm.org/D20565

llvm-svn: 273547