gd: propagate image format dependencies

After f8bdd7969d it has become necessary for users
of gd to also add inputs for optional image format support, such as libjpeg and
libwebp.

This patch makes the following commits obsolete:
- 972c438c03
- 2113b7389a
- 94286527ac
- a371094f1f
- f345d01974

pkgs/development/libraries/gd/default.nix

@@ -1,9 +1,9 @@
 { stdenv, fetchurl
 , pkgconfig
 , zlib
-, libjpeg
 , libpng
-, libwebp
+, libjpeg ? null
+, libwebp ? null
 , libtiff ? null
 , libXpm ? null
 , fontconfig
@@ -20,7 +20,8 @@ stdenv.mkDerivation rec {
   };
 
   nativeBuildInputs = [ pkgconfig ];
-  buildInputs = [ zlib fontconfig freetype libjpeg libpng libwebp libtiff libXpm ];
+  buildInputs = [ zlib fontconfig freetype ];
+  propagatedBuildInputs = [ libpng libjpeg libwebp libtiff libXpm ];
 
   outputs = [ "dev" "out" "bin" ];