CMake: bump min CMake version to 3.18 or remove usage of `check_linker_flag()`

[SpaceIm]

#3392 (part of zstd 1.5.4) checks linker flags in CMake build by relying on https://cmake.org/cmake/help/latest/module/CheckLinkerFlag.html, a function available since CMake 3.18. But cmake_minimum_required() of main CMakeLists is still 2.8.12.
Is it intentional to use such recent feature? If it is, cmake_minimum_required() should be updated accordingly. Otherwise it's possible to achieve the same checks by using check_source_compiles() and therefore avoid constraining CMakeLists of zstd to such recent CMake version.

[Cyan4973]

We could update the minimum version of cmake if there is a good reason for it, but 3.18 is way too recent to become the new minimum (I think we could consider a new minimum as high as 3.5, but no more than that to ensure a good reach).

When a feature requires a version which is higher than the minimum, it should be guarded by version checks, and offer a fallback strategy.

#3392 was added by @terrelln , so we'll need his input.

[botanegg]

To anyone who is stuck with CI pipelines - you can upgrade your cmake from kitware apt - https://apt.kitware.com/
Look at kitware-archive.sh
This solved the problem for me

[kou]

How about just disabling the -z noexecstack with old CMake?
I want to use old CMake for apache/arrow.
See also: apache/arrow#34148

[terrelln]

How about just disabling the -z noexecstack with old CMake?

It should be safe to default to not adding the linker flag if the cmake version is too old. This PR was mostly aiming at fixing our tests, and it should be safe to skip this flag when cmake doesn't support check_linker_flag(). I'll put up a PR to add that.

[kou]

@terrelln Thanks for your comment! #3510 does it. Could you review the pull request?