[gimp] build: build libjxl to sync nightly and beta flatpak manifest.

[Jehan <jehanp src gnome org>]

commit 6107ae17c93a7f711c73b5923fa48f4189dcb1be
Author: Jehan <jehan girinstud io>
Date:   Fri Oct 1 23:09:50 2021 +0200

    build: build libjxl to sync nightly and beta flatpak manifest.
    
    See commit e9f790e1ff8d50f63933ec0b0fbb9325447324d4 on Flathub's beta
    flatpak repository.

 build/flatpak/org.gimp.GIMP-nightly.json | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
---
diff --git a/build/flatpak/org.gimp.GIMP-nightly.json b/build/flatpak/org.gimp.GIMP-nightly.json
index bac55636cf..47d2995752 100644
--- a/build/flatpak/org.gimp.GIMP-nightly.json
+++ b/build/flatpak/org.gimp.GIMP-nightly.json
@@ -393,6 +393,32 @@
                 }
             ]
         },
+        {
+            "name": "libjxl",
+            "config-opts": [
+                "-DJPEGXL_ENABLE_PLUGINS=OFF",
+                "-DBUILD_TESTING=OFF",
+                "-DJPEGXL_WARNINGS_AS_ERRORS=OFF",
+                "-DJPEGXL_ENABLE_SJPEG=OFF",
+                "-DJPEGXL_ENABLE_BENCHMARK=OFF",
+                "-DJPEGXL_ENABLE_EXAMPLES=OFF",
+                "-DJPEGXL_ENABLE_MANPAGES=OFF",
+                "-DJPEGXL_ENABLE_SKCMS=ON",
+                "-DJPEGXL_ENABLE_JNI=OFF",
+                "-DJPEGXL_ENABLE_TCMALLOC=OFF",
+                "-DJPEGXL_ENABLE_TOOLS=OFF"
+            ],
+            "buildsystem": "cmake-ninja",
+            "builddir": true,
+            "sources": [
+                {
+                    "type": "git",
+                    "url": "https://github.com/libjxl/libjxl.git";,
+                    /* Last commit on v0.6.x branch at time of writing. */
+                    "commit": "20cccbf646158cb128d68db20d12f93d1fb9b6a1"
+                }
+            ]
+        },
         {
             "name": "luajit",
             "no-autogen": true,