That build went OK (I didn't install it) and I may have figured out my original problem (possibly ambiguous C++ overload resolution). So I wanted to go back to the released version of 5.7.0 and try what I found there, but...

The release version of QtCreator doesn't work any more. It starts up, but when I try to open the old project, nothing happens. (No, wait, that's not exactly true...I'm playing with QtCreator in another window, and there's something wrong with screen updating. I opened the project and nothing happened, but when I minimize then restore the window, some of the panes are updated as expected. However, I can't get the UI designer GUI to show up, and the source-list viewer won't expand folders or show source files.)

It seems like one of the system libraries I installed during the Git compile process broke something in the 5.7.0 release installation, but there are no error messages or other indications of what is wrong.

Does this sound familiar to anyone? I'm afraid I may have to install a new Linux machine and start over again!