[CRITICAL BUGFIX] Fix a significant oversight in **GrackleConfig.cmake**

[mabruzzo]

This PR fixes a significant bug in GrackleConfig.cmake that causes applications with CMake-build systems that expect to link against free-standing installations of Grackle (i.e. Grackle is pre-built) to break when using the newest versions of CMake (version 4.0 or newer).

Background

As part of the installation-process, the CMake build-system installs a file called GrackleConfig.cmake alongside the Grackle headers and libraries. This is a special kind CMake script that a build-system searches for and reads when you want to building a downstream application that links against a free-standing Grackle installation. Basically, the script contains queryable metadata about how Grackle was configured and the necessary linker/compilation flags.

While we require version 3.16 of CMake or newer to actually build/install the core Grackle library, I followed standard convention and tried to make it possible for the GrackleConfig.cmake file to be used by CMake 3.3 (basically as early a version of CMake as possible).

• Essentially, the idea is that the version used to compile/package a version of Grackle may exceed the version of CMake currently installed on somebody's machine. (This isn't a significant consideration for us right now, but it's worth thinking about for the future)
• To put it another way, since the GrackleConfig.cmake file is a really simple script, it wasn't hard to use a subset of the language that was compatible with older versions of the lanugage.

The Problem

I mistakenly used the cmake_minimum_version command within GrackleConfig.cmake to ensure that the file wasn't read by a version of CMake older than 3.3.

Everything seemed to work fine at first. I only realized this was an issue today. It turns out that with the release of CMake 4.0 (released at the end of March), that calling cmake_minimum_version to try enforce a minimum version before version 3.5 now causes CMake to abort with an error.

Consequently, people can use CMake 4.0 (or newer) to perform a full standalone installation of Grackle. However, if they then turn around and try to link against that version of Grackle (with that same CMake version), CMake will abort with an error. It's worth noting that doing an embedded install of Grackle (e.g. compiling Grackle as part of the downstream application) using CMake won't cause any problems, but the scenario I highlighted is an extremely plausible way of using CMake.

The Solution

Fixing this is easy. We simply delete the call to
cmake_minimum_version in the GrackleConfig.cmake file. For whatever reason I had previously written a separate redundant check enforcing the minimum CMake version that we can leave in place.

Ramifications

I really think we should consider making a 3.4.1 release of grackle with this bugfix. This is only going to be a bigger problem as time goes on (and people start using newer versions of CMake)

[brittonsmith]

I'll merge this now. I agree we should probably issue a quick bugfix release.