Sorter conversion to function pointer does not work with MSVC

[Morwenn]

After a couple of fixes of my side, the latest version of MSVC is finally able to mostly compile cpp-sort and will be considered officially supported for the 1.10.0 release. However, there are still a few remaining issues, and that one might be the biggest one: conversion from sorter to function pointer simply does not work. I already had the hardest time to get it to work in a portable manner between both GCC and Clang, so I fear that I won't try to solve it for MSVC so soon.

The failing tests were simply and changed or disabled for MSVC for now.