[ObjectYAML] Support for DWARF line tables

This patch re-lands r291470, which failed on Linux bots. The issue (I believe) was undefined behavior because the size of llvm::dwarf::LineNumberOps was not explcitly specified or consistently respected. The updated patch adds an explcit underlying type to the enum and preserves the size more correctly.

Original description:

This patch adds support for the DWARF debug_lines section. The line table state machine opcodes are preserved, so this can be used to test the state machine evaluation directly.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@291541 91177308-0d34-0410-b5e6-96231b3b80d8