Don't require CMake 3.18 or later

[kou]

fix #3500

CMake 3.18 or later was required by #3392. Because it uses CheckLinkerFlag. But requiring CMake 3.18 or later is a bit aggressive. Because Ubuntu 20.04 LTS still uses CMake 3.16.3: https://packages.ubuntu.com/search?keywords=cmake

This change disables -z noexecstack check with old CMake. This will not break any existing users. Because users who need -z noexecstack must already use CMake 3.18 or later.

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[botanegg]

Instead of just disable this flag it can be done by try_compile like this:
https://github.com/mctools/ncrystal/blob/a263fb0efa4550239ef9fe7bb22e63d951d56206/CMakeLists.txt#L201-L216

[kou]

The shim implementation will increase maintenance cost a bit.
Do we need to implement it?

The author of #3392 uses CheckLinkerFlag. It seems that users who need this feature use newer CMake. So the shim implementation may not be needed for real users.

If the shim implementation is needed for this project, I can do it.

[terrelln]

Thanks for the PR @kou!

[terrelln]

I think it is reasonable to simply disable the extra ldflags when check_linker_flags() is not available, since the only flags we currently use are optional.

I think we should just add a comment to the function to clarify that the ldflags don't get added for old cmake versions.

[terrelln]

Can you just add a comment to this function that says that it doesn't add ldflags for older cmake versions? In case that we need to add other ldflags that are non-optional later.

[kou]

It makes sense. I've add a comment:

        # We never add a linker flag with CMake < 3.18. We will
        # implement CHECK_LINKER_FLAG() like feature for CMake < 3.18
        # or require CMake >= 3.18 when we need to add a required
        # linker flag in future.

Does this make sense?

[terrelln]

Thanks @kou!

[kou]

@terrelln Thanks! Do you have a plan to release a new version with this change soon? (If it's done, apache/arrow can use the latest Zstandard. But it's not a blocker. So apache/arrow can wait a new version.)