After two day of work, I cannot get CB to compile using gtk3, much less solve the MouseSap plugin problems (using Mint 19 based on gtk3).
So..., I'll remove all use of gtk from MouseSap to get it to work under windows and Linux gtk2 and disable it for use under gtk3 until CB itself compiles using gtk3.
I'm just not savvy enough on Linux to solve the gtk3 compiler errors in scintilla.