SDL2_ttf: record provided pkg-config modules in meta

This is verified using testers.hasPkgConfigModules which leads to a
slight refactor of the expression.

pkgs/development/libraries/SDL2_ttf/default.nix

···
-{ lib, stdenv, pkg-config, darwin, fetchurl, SDL2, freetype, harfbuzz, libGL }:
+{ lib, stdenv, pkg-config, darwin, fetchurl, SDL2, freetype, harfbuzz, libGL, testers }:
 
-stdenv.mkDerivation rec {
+stdenv.mkDerivation (finalAttrs: {
   pname = "SDL2_ttf";
   version = "2.20.2";
 
   src = fetchurl {
-    url = "https://www.libsdl.org/projects/SDL_ttf/release/${pname}-${version}.tar.gz";
+    url = "https://www.libsdl.org/projects/SDL_ttf/release/${finalAttrs.pname}-${finalAttrs.version}.tar.gz";
     sha256 = "sha256-ncce2TSHUhsQeixKnKa/Q/ti9r3dXCawVea5FBiiIFM=";
   };
 
···
     ++ lib.optional (!stdenv.isDarwin) libGL
     ++ lib.optional stdenv.isDarwin darwin.libobjc;
 
+  passthru.tests.pkg-config = testers.hasPkgConfigModules {
+    package = finalAttrs.finalPackage;
+  };
+
   meta = with lib; {
     description = "Support for TrueType (.ttf) font files with Simple Directmedia Layer";
     platforms = platforms.unix;
     license = licenses.zlib;
     homepage = "https://github.com/libsdl-org/SDL_ttf";
+    pkgConfigModules = [ "SDL2_ttf" ];
   };
-}
+})