[gnome-builder] flatpak: use meson for libgit2-glib

[Sébastien Lafargue <slafargue src gnome org>]

commit 36ccf406008ae86fe91c104369a15c29bbbf8af9
Author: Sebastien Lafargue <slafargue gnome org>
Date:   Wed Feb 7 13:32:04 2018 +0100

    flatpak: use meson for libgit2-glib
    
    libgit2-glib has removed the autotools build system:
    https://git.gnome.org/browse/libgit2-glib/commit/?id=572d590894c089a12f6e133fedfc5424d8f0a274
    
    We switch to meson in our manifest.

 build-aux/flatpak/org.gnome.Builder.json | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/build-aux/flatpak/org.gnome.Builder.json b/build-aux/flatpak/org.gnome.Builder.json
index f82d02309..ab281cb36 100644
--- a/build-aux/flatpak/org.gnome.Builder.json
+++ b/build-aux/flatpak/org.gnome.Builder.json
@@ -481,6 +481,12 @@
         },
         {
             "name" : "libgit2-glib",
+            "config-opts" : [
+                "--libdir=/app/lib",
+                "--buildtype=debugoptimized"
+            ],
+            "buildsystem" : "meson",
+            "builddir" : true,
             "sources" : [
                 {
                     "type" : "git",