[gnome-builder] build: use G_SLICE=always-malloc in flatpak

[Christian Hergert <chergert src gnome org>]

commit 5e81b205e450ddbf9e652de317a4e0f46fb3c594
Author: Christian Hergert <chergert redhat com>
Date:   Mon Jul 23 16:15:55 2018 -0700

    build: use G_SLICE=always-malloc in flatpak
    
    We use tcmalloc instead of glibc malloc when shipping flatpaks. So lets
    also disable GSlice which has no benefit over tcmalloc performance or
    space wise as tcmalloc employs similar SLAB/arena techniques.

 build-aux/flatpak/org.gnome.Builder.json | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/build-aux/flatpak/org.gnome.Builder.json b/build-aux/flatpak/org.gnome.Builder.json
index 205ef4a74..56a11ce33 100644
--- a/build-aux/flatpak/org.gnome.Builder.json
+++ b/build-aux/flatpak/org.gnome.Builder.json
@@ -38,7 +38,8 @@
         "--filesystem=/etc/ca-certificates:ro",
         "--filesystem=~/.local/share/flatpak",
         "--filesystem=xdg-data/meson",
-        "--filesystem=/var/lib/flatpak"
+        "--filesystem=/var/lib/flatpak",
+        "--env=G_SLICE=always-malloc"
     ],
     "x-run-args" : [
         "--standalone",