Revert "Temporarily Revert "[gicombiner] Add the MatchDag structure and parse instruction DAG's from the input""

This reverts commit e62e760f29567fe0841af870c65a4f8ef685d217.

The issue @uweigand raised should have been fixed by iterating over the
vector that owns the operand list data instead of the FoldingSet.

The MSVC issue raised by @thakis should have been fixed by relaxing the
regexes a little. I don't have a Windows machine available to test that so
I tested it by using `perl -p -e 's/0x([0-9a-f]+)/\U\1\E/g' to convert the
output of %p to the windows style.

I've guessed at the issue @phosek raised as there wasn't enough information
to investigate it. What I think is happening on that bot is the -debug
option isn't available because the second stage build is a release build.
I'm not sure why other release-mode bots didn't report it though.