[gnome-builder] build-aux: use FLATPAK_BUILDER_BUILDDIR in flatpak manifest

[Christian Hergert <chergert src gnome org>]

commit 6fc3ebc02edbac8415d8802fbbb0f850da3162e3
Author: Christian Hergert <chergert redhat com>
Date:   Fri Jul 22 11:40:17 2022 -0700

    build-aux: use FLATPAK_BUILDER_BUILDDIR in flatpak manifest

 org.gnome.Builder.Devel.json | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/org.gnome.Builder.Devel.json b/org.gnome.Builder.Devel.json
index 9c3b0ec42..aa5b60950 100644
--- a/org.gnome.Builder.Devel.json
+++ b/org.gnome.Builder.Devel.json
@@ -134,7 +134,7 @@
                 "/bin/ulockmgr_server"
             ],
             "post-install" : [
-                "install -m a+rx build-aux/flatpak/fusermount-wrapper.sh /app/bin/fusermount"
+                "install -m a+rx ${FLATPAK_BUILDER_BUILDDIR}/build-aux/flatpak/fusermount-wrapper.sh 
/app/bin/fusermount"
             ],
             "sources" : [
                 {