Reformat and hoist section grabbing to top level.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190648 91177308-0d34-0410-b5e6-96231b3b80d8
Add initial support for handling gnu style pubnames accepted by some
versions of gold. This support is designed to allow gold to produce
gdb_index sections similar to the accelerator tables and consumable
by gdb.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@190649 91177308-0d34-0410-b5e6-96231b3b80d8