COFF: Add support for Dwarf accelerator tables.

This allows COFF targets to emit accelerator tables
when requested by -dwarf-accel-tables=Enable instead
of aborting. The test DebugInfo/cross-cu-inlining.ll
covers this on COFF platforms.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222034 91177308-0d34-0410-b5e6-96231b3b80d8