Changing case to -f parameter causes no regeneration for CMake projects on macOS

[KyleFromKitware]

Let's say you have the following minimal CMake project:

cmake_minimum_required(VERSION 3.18)
project(test NONE)

Then you run the following on macOS:

$ mkdir build
$ cd build
$ cmake .. -G "Ninja Multi-Config"
$ ninja -f build-debug.ninja # This correctly says "ninja: no work to do."
$ touch ../CMakeLists.txt
$ ninja -f build-debug.ninja # This should cause a reconfigure, but still says no work to do
$ ninja -f build-Debug.ninja # This reconfigures correctly

This leads me to believe Ninja isn't handling case-insensitive filesystems correctly. build-Debug.ninja is the actual name of the file, but I would not expect passing build-debug.ninja to cause different behavior.

This was first reported here:

https://gitlab.kitware.com/cmake/cmake/-/issues/22070

[bradking]

Cc: @mathstuf