Re-reapply "[DebugInfo] Use variadic debug values to salvage BinOps and GEP...

Re-reapply "[DebugInfo] Use variadic debug values to salvage BinOps and GEP instrs with non-const operands"

Previous build failures were caused by an error in bitcode reading and
writing for DIArgList metadata, which has been fixed in e5d844b5.
There were also some unnecessary asserts that were being triggered on
certain builds, which have been removed.

This reverts commit dad5caa5.