CMake 3.12 really necessary? about devilutionx

[AJenbo]

The requirment has now been lowered to 3.7 for most platforms, technically it works all the way back to and including 3.3. But using older versions then 3.7 for continuous testing seems more of a hassle then it's worth, and it's preferable that we can detect if there is a change in requirements.

For Windows-builds the limit is 3.10 since older versions fail during the pthread lookup.

#50

[AJenbo]

The requirement comes from the Windows build. We build the releases on Debian-backports (CMake 3.13). Prior to adding Windows support the CMake requirement was 3.7.

We are currently looking in to ways of bringing down the requirement to something like 3.10, or maybe even 3.7. Thanks for the version overview.

[grepwood]

@AJenbo What specifically about the Windows build warranted this change? I can crosscompile OpenJK for Windows just fine with CMake 3.9.