CMake Ninja build produces 100's of warnings

[MiCurry]

While Ninja is not a commonly used generator for ModEM, building with Ninja produces hundreds of Warning: missing terminating ' character warnings.

Reproduce:

$ mkdir build-ninja
$ cd build-ninja
$ cmake .. -DCMAKE_Fortran_COMPILER=mpifort -G Ninja
$ ninja

This was found by @tjhei in #30 (comment) and is mentioned in this CMake Issue: https://gitlab.kitware.com/cmake/cmake/-/issues/17466#note_438832.

The solution for this will be renaming all .f90 file extensions to .F90. It's a bit annoying that CMake and Ninja don't respect the -fpp / -cpp, but I'm making this issue to keep a record of the issue.

At this point, I don't see a point in making this change, unless we start to get requests to do so. Making it as wontfix for now.