So I've started getting my toolchain together for working on WinMerge + Qt. For anyone interested, I have Kimmo's test project built and running on my MacBook. I initially started using Netbeans, which has Qt support, but ended up using Xcode.
Come to find out that qmake on mac outputs a .xcodeproj file by default, so that seemed like the easier option. Indeed it was pretty easy to build the project, and QScintilla built easily also. The one thing I had problems with was getting the final app to find libqscintilla2. I'm currently just copying it to the app directory, I'll post here when I figure out where to specify this in the project settings, because the obvious search path settings didn't seem to work.
Anyway, just wanted to share my findings,