Get an old (or new) toothbrush and your favorite spray cleaner/degreaser and clean/brush out the thread of the adjuster bolt too. It is amazing how much road grime get deep down into the fine threads of that bolt. IMHO that is what freezes up the adjuster bolt in other than snow/salt corrosion country.
After cleaning out the threads like this I have unscrewed that bolt by hand in some, not all, junkyard cars.

Worst case you can raise the front end and support with jack stands and cut the adjuster in half with a grinder and disk. Then you can lift the threaded nut/plate out of the lower control arm and try and get the rest of the bolt out of it if you want.

It is a lot easier to just by a new one of those when you get the new bolt.