The p11-kit-trust test looks in /usr/lib for pkcs11 modules. As a result it is unnecessarily skipped on sandboxed builds, and fails on unsandboxed builds with a system p11-kit. Replace hard-coded /usr/lib paths with pkg-config.

Motivation for this change

p11-kit-trust test was failing on my unsandboxed build because the system p11-kit-trust module was found instead, and skipped on normal builds because it wasn't looking in p11_kit. pkg-config knows where it is and tests pass in both cases.

Happy to change if there's a better way to search for this library (e.g., $buildInputs or patch in hard-coded path) or it would be better to just force skip the test regardless.

This test does not exist (in this form anyway) in gnutls 3.5.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option build-use-sandbox in nix.conf on non-NixOS)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nox --run "nox-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Fits CONTRIBUTING.md.