tkinter/matplotlib: mark tkinter broken if missing, omit from matplotlib

[ghost]

Description of changes

The tkinter derivation apparently downloads binaries rather than
building from source. Let's mark the package broken on platforms for
which no binaries are available.

Let's also omit tkinter support from matplotlib on platforms where
tkinter is broken.

Things done

• Built on platform(s)
  • powerpc64le-linux
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• 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/)
• Fits CONTRIBUTING.md.

[ghost]

Ping...

[FRidh]

It should inherit this meta from the base Python derivation from which the tkinter module is taken.

[FRidh]

tkinter is built from source. py is pythonXYFull. So, if pythonXYFull is built for Power64 and that built comes with tkinter, then this tkinter derivation will copy that part.