nix: build improvements

[andresilva]

Describe your PR, what does it fix/add?

Fixes populating the version header and removes unused stuff.

Is there anything you want to mention? (unchecked code, possible bugs, found problems, breaking compatibility, etc.)

No.

Is it ready for merging, or does it need work?

Yes.

[fufexan]

@vaxerski are you alright with the hyprland.pc.in changes? CMake now installs the wlroots headers under @PREFIX@/include/hyprland/wlr. Only meson still installs them to wlroots-hyprland, but I'll change it.

Tested building the plugins, all green.

[vaxerski]

dont care, as long as shit works

[Agent00Ming]

On arch:

./documents/git/hyprland/build/hyprpm/hyprpm update

! Cloning https://github.com/hyprwm/hyprland, this might take a moment.                                                                                                                                   
✔ cloned                                                                                                                                                                                                  
✔ checked out to running ver                                                                                                                                                                              
! configuring Hyprland                                                                                                                                                                                    
✔ configured Hyprland                                                                                                                                                                                     
✖ failed to install headers with error code 4                                                                                                                                                             
 ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━  5 / 5  Failed                                                                                                                                        

✖ Headers version mismatch. Please run hyprpm update to fix those.

not sure if this is good or bad

[fufexan]

I hate that error code. I need more info. Thanks for testing though.

Oh, the hyprland-git pkgbuild still uses Meson. I'll fix that too.

[fufexan]

I've decided the pkg-config stuff + meson are out of scope for this PR, and I'll open a new one for those. Merging as soon as CI passes.