libffi: Add meta.pkgConfigModules

pkgs/development/libraries/libffi/default.nix

···
 , doCheck ? !(stdenv.hostPlatform.isStatic)
 , dejagnu
 , nix-update-script
+, testers
 }:
 
-stdenv.mkDerivation rec {
+stdenv.mkDerivation (finalAttrs: {
   pname = "libffi";
   version = "3.4.4";
 
   src = fetchurl {
-    url = "https://github.com/libffi/libffi/releases/download/v${version}/${pname}-${version}.tar.gz";
+    url = with finalAttrs; "https://github.com/libffi/libffi/releases/download/v${version}/${pname}-${version}.tar.gz";
     sha256 = "sha256-1mxWrSWags8qnfxAizK/XaUjcVALhHRff7i2RXEt9nY=";
   };
 
···
 
   passthru = {
     updateScript = nix-update-script { };
+    tests = {
+      pkg-config = testers.hasPkgConfigModules {
+        package = finalAttrs.finalPackage;
+      };
+    };
   };
 
   meta = with lib; {
···
     license = licenses.mit;
     maintainers = with maintainers; [ matthewbauer ];
     platforms = platforms.all;
+    pkgConfigModules = [ "libffi" ];
   };
-}
+})