cmake: setup-hook.sh: add genCmakeDefaultFlags()

[ShamrockLee]

Description of changes

This PR extracts the default CMake flags pretending code into its own Bash function genCmakeDefaultFlags(). Instead of pretending the flags to cmakeFlags, it collects them into a global Bash array cmakeDefaultFlags.

Original discussions:
#318614 (comment)
#299622 (comment)

Cc: @AndersonTorres @jtojnar @wolfgangwalther

Things done

• Built on platform(s)
  • x86_64-linux (built cmakeMinimal)
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandboxing enabled in nix.conf? (See Nix manual)
  • sandbox = relaxed
  • sandbox = true
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 24.11 Release Notes (or backporting 23.11 and 24.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

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[ShamrockLee]

@ofborg build cmake

[ShamrockLee]

@ofborg build cmakeMinimal

[ShamrockLee]

I adjusted the style and changed the order to group all the non-conditional flags.

@wolfgangwalther, what do you think about the current style?

[wolfgangwalther]

The first two commits LGTM. We'll need to assume that the order of flags for cmake doesn't matter, though.

The last commit says:

This enables developers to get the default CMake flags provided by Nixpkgs without having to use cmakeConfigurePhase.

I don't understand the reason for that last commit, yet. Why is that important, what would you do with those flags?

[ShamrockLee]

The last commit says:

This enables developers to get the default CMake flags provided by Nixpkgs without having to use cmakeConfigurePhase.

I don't understand the reason for that last commit, yet. Why is that important, what would you do with those flags?

In a build flow where other build tools control CMake, the package developer needs to configure the command-line arguments for CMake without executing CMake itself. A Bash function to provide the flags without running the whole cmakeConfigurePhase might be helpful in such circumstances.

Update: Such use cases are essentially edge cases. I shouldn't emphasize them too much.

[wolfgangwalther]

First two commits LGTM. Only eye-balled the changes, did not build anything with it.

Last commit I can't say much about the usefulness, but it shouldn't do any harm.

[ShamrockLee]

Would it sound more clearly if the function is called setCmakeDefaultFlags?