Some edge cases for C++

Hi,

I have had a chance to use this day-to-day now with C++ code I am working on. It mostly works really well! Really nice to have only functions fold.

I found a few edge cases, so I made some more tests. I pushed them to my repo here:
https://github.com/CallumHoward/folding_tests/compare/cca2c3f...dee8229?diff=unified&name=dee8229