llvm-dwarfdump: Add support for dumping the .debug_loc section

This is a basic implementation - we still don't have any support (that I
know of) for dumping DWARF expressions in a meaningful way, so the
location information itself is just printed as a sequence of bytes as we
do elsewhere.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@184361 91177308-0d34-0410-b5e6-96231b3b80d8