DebugInfo: Refactor high_pc/low_pc construction into reusable function

For incoming improvements to inlined functions and lexical blocks
suggested by Adrian Prantl in review of r203187.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203263 91177308-0d34-0410-b5e6-96231b3b80d8
MC: Use MachO::SectionType for MCSectionMachO::getType's return type

This is a straightfoward replacement, it makes debugging a little
easier.

This has no functional impact.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@203264 91177308-0d34-0410-b5e6-96231b3b80d8