libiio: disable Python for static builds

[lopsided98]

Description of changes

libiio's Python bindings use ctypes to load the shared library, which obviously can't work with a static build. Recent changes (#240575, #244118) have also started causing eval errors because the package uses stdenv.hostPlatform.extensions.sharedLibrary, which isn't available when building a static library:

 error:
       … while calling the 'derivationStrict' builtin

         at /builtin/derivation.nix:9:12: (source not available)

       … while evaluating derivation 'ardupilot-copter-bebop-static-armv7l-unknown-linux-musleabihf-35da15d'
         whose name attribute is located at /nix/store/sralzj4w34v4mwr0sxq417b4ys202in3-source/pkgs/stdenv/generic/make-derivation.nix:300:7

       … while evaluating attribute 'propagatedBuildInputs' of derivation 'ardupilot-copter-bebop-static-armv7l-unknown-linux-musleabihf-35da15d'

         at /nix/store/sralzj4w34v4mwr0sxq417b4ys202in3-source/pkgs/stdenv/generic/make-derivation.nix:354:7:

          353|       depsHostHostPropagated      = lib.elemAt (lib.elemAt propagatedDependencies 1) 0;
          354|       propagatedBuildInputs       = lib.elemAt (lib.elemAt propagatedDependencies 1) 1;
             |       ^
          355|       depsTargetTargetPropagated  = lib.elemAt (lib.elemAt propagatedDependencies 2) 0;

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: attribute 'sharedLibrary' missing

       at /nix/store/sralzj4w34v4mwr0sxq417b4ys202in3-source/pkgs/development/libraries/libiio/default.nix:64:38:

           63|     # Hardcode path to the shared library into the bindings.
           64|     sed "s#@libiio@#$lib/lib/libiio${stdenv.hostPlatform.extensions.sharedLibrary}#g" ${./hardcode-library-path.patch} | patch -p1
             |                                      ^
           65|

This patch adds a flag to disable the Python bindings, and automatically disables them for static builds.

Note that even with this patch, static libiio doesn't build successfully by default. You have to disable avahi and manually disable libxml2 with custom CMake flags. I currently build a custom stripped down static libiio like this:

(pkgsStatic.libiio.override {
  avahiSupport = false;
  libxml2 = null;
  libusb1 = null;
}).overrideAttrs ({
  cmakeFlags ? [], ...
}: {
  cmakeFlags = cmakeFlags ++ [
    "-DWITH_NETWORK_BACKEND=OFF"
    "-DWITH_USB_BACKEND=OFF"
    "-DWITH_XML_BACKEND=OFF"
  ];
})

cc @thoughtpolice @amjoseph-nixpkgs

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• 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/)
• 23.11 Release Notes (or backporting 23.05 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.