Add support for newer DWARF fields to ldscript

[imp]

This is obsolete, but I'll commit the meat of it. See D44072. Minor other bits in other commits, but they weren't pulled directly from here.

[emaste]

sys/conf/ldscript.amd64

236–238

It loooks like GNU has dropped these?

[imp]

sys/conf/ldscript.amd64

236–238

Do you have a reference? I couldn't find anything in our tree, but I may have
overlooked something there or in my overly-hasty google search.