[gnome-builder] meson: allow using $NINJA for ninja path

[Christian Hergert <chergert src gnome org>]

commit 93c809b86ab4ae6c3bd8a97ae4fe1715a95f4bbf
Author: Christian Hergert <chergert redhat com>
Date:   Wed Oct 24 13:49:23 2018 -0700

    meson: allow using $NINJA for ninja path

 src/plugins/meson/gbp-meson-pipeline-addin.c | 3 +++
 1 file changed, 3 insertions(+)
---
diff --git a/src/plugins/meson/gbp-meson-pipeline-addin.c b/src/plugins/meson/gbp-meson-pipeline-addin.c
index c719d5c75..1f6a978e1 100644
--- a/src/plugins/meson/gbp-meson-pipeline-addin.c
+++ b/src/plugins/meson/gbp-meson-pipeline-addin.c
@@ -102,6 +102,9 @@ gbp_meson_pipeline_addin_load (IdeBuildPipelineAddin *addin,
         }
     }
 
+  if (ninja == NULL)
+    ninja = ide_configuration_getenv (config, "NINJA");
+
   if (ninja == NULL)
     {
       ide_context_warning (context,