[FaultMaps] Add a parser for the __llvm__faultmaps section.

Summary:
The parser is exercised by llvm-objdump using -print-fault-maps.  As is
probably obvious, the code itself was "heavily inspired" by
http://reviews.llvm.org/D10434.

Reviewers: reames, atrick, JosephTremoulet

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D10491

llvm-svn: 240304