[CMake] When CMake re-runs with Ninja on Windows, it switches to Debug build type

[Antoine Pitrou]

Hello,

I am having a weird issue on Windows when Ninja is used as a generator.

As you can see below:
https://ci.appveyor.com/project/pitrou/arrow/build/job/owq89j34spl9hy4d#L584

the build is first configured in Release mode as requested on the
command-line.

But for some reason CMake decides to re-run itself (it thinks
CMAKE_CXX_COMPILER has changed, even though it hasn't) and switches the
build to Debug mode:
https://ci.appveyor.com/project/pitrou/arrow/build/job/owq89j34spl9hy4d#L839

What could be the reason the build type isn't kept the same?

Regards

Antoine.