Ok, I may be an idiot. Maybe even the village idiot. Let's just get that out of the way from the start.
I'm smart enough to get in trouble, which is where I am now.
In my infinite wisdom, I tried to load the appropriate STM32F7 drivers in an attempt to up my game from 8 bit to 32 bit controllers.
I have a lot of experience with the 8 bit stuff and use the Mega in professional projects at work. Many tens of thousands of lines of code written. Running 1.6.7 because of compatibility issues.
Since I made the 32 bit attempt, I am having an issue with the 8 bit programs. They compile and load, but do not compile properly.
I did some deep thinking on this and restored to a previous day prior to the 32 bit affair and things worked again after I deleted the arduino15 file contents and did a board update.
Not happy enough with that, I tried with the 32 bit affair once again and now have the same issue, but restore now has no effect in a positive direction.
Then I removed the installation of 1.6.7 and reloaded. No change to the compile issue.
I'm one big ear for suggestions! A preemptive comment - I can compile and load, but somehow the compile is not right and prevents the programs that previously worked flawlessly for functioning properly.