gflags: repairing all the things

If I've screwed up ``` gflags ``` as much as #34528 makes it look like, here's a bunch of reverts to deal with it. The maintainers may be in a better position to revert things rather than just pasting the old formula atop the new one as I've done here, so close as desired, but given I may have screwed up ``` gflags ``` and co I felt I should at least try and fix it :grin:.