[cmake] Do not set CMP0048 explicitly

[gruenich]

Since CMake 3.0 it is set implicitly to NEW, cppcheck requires CMake 3.5

https://cmake.org/cmake/help/latest/policy/CMP0048.html

[firewave]

Since CMake 3.0 it is set implicitly to NEW, cppcheck requires CMake 3.5

The documentation says that the policy was introduced with 3.0. and the behavior is actually documented as the opposite you are suggesting:

If it is not set, CMake warns, and uses OLD behavior.

This is supported by the project() at https://cmake.org/cmake/help/latest/command/project.html#options:

VERSION <version>

    Optional; may not be used unless policy CMP0048 is set to NEW.

I also checked all the individual release notes and there is no mention of this policy since it was introduced. I am having issues using the Wayback Machine so I could not check if the documentation changed over time.

But this does not match the behavior at all as it seems to work as intended (I am not 100% sure we test for the correct version somewhere) and no warning is written.

I always found these policies extremely confusing and not sufficiently documented (in some cases it always seemed impossible for them to work) when I had to deal with them. So no surprise here...

[gruenich]

I always found these policies extremely confusing

I know what you mean. To me reading
https://cmake.org/cmake/help/latest/manual/cmake-policies.7.html#introduction
always help to end my confusion.

CMP0048 was introduced with CMake 3.0, as this version changed the way to handle version variables. In case the required minimum CMake version was below 3.0, the policy was set to OLD. As cppcheck requires CMake 3.5, the policy is already set to NEW. I.e., my merge request removes a no-op.

Regarding CMP0048, as cppcheck set the project version when calling the project command, cppcheck is not affected anyways.

[gruenich]

Any reason to not merge this? Should I explain anything in more detail?