[gnome-todo] Revert "Revert "flatpak: Also build GTK4""

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 5a72af9a49228521d3d111cebf22387f0e8d2fdf
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Wed May 6 15:04:17 2020 -0300

    Revert "Revert "flatpak: Also build GTK4""
    
    This reverts commit fb7c216b0613b1341c96f90f63882eaabddca84b.

 build-aux/flatpak/org.gnome.Todo.json | 47 +++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
---
diff --git a/build-aux/flatpak/org.gnome.Todo.json b/build-aux/flatpak/org.gnome.Todo.json
index b19db31..599f940 100644
--- a/build-aux/flatpak/org.gnome.Todo.json
+++ b/build-aux/flatpak/org.gnome.Todo.json
@@ -157,6 +157,53 @@
                 }
             ]
         },
+        {
+            "name" : "libsass",
+            "buildsystem" : "meson",
+            "builddir" : true,
+            "config-opts": [
+                "--libdir=/app/lib"
+            ],
+            "sources" : [
+                {
+                    "type" : "git",
+                    "url" : "https://github.com/lazka/libsass.git";,
+                    "branch" : "meson"
+                }
+            ]
+        },
+        {
+            "name" : "sassc",
+            "buildsystem" : "meson",
+            "builddir" : true,
+            "config-opts": [
+                "--libdir=/app/lib"
+            ],
+            "sources" : [
+                {
+                    "type" : "git",
+                    "url" : "https://github.com/lazka/sassc.git";,
+                    "branch" : "meson"
+                }
+            ]
+        },
+        {
+            "name": "gtk",
+            "buildsystem": "meson",
+            "builddir": true,
+            "config-opts": [
+                "-Ddemos=false",
+                "-Dbuild-examples=false",
+                "-Dbuild-tests=false",
+                "--libdir=/app/lib"
+            ],
+            "sources": [
+                {
+                    "type": "git",
+                    "url": "https://gitlab.gnome.org/GNOME/gtk.git";
+                }
+            ]
+        },
         {
             "name" : "gnome-todo",
             "buildsystem" : "meson",