[mutter] ci: Test building without native backend support

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 06a7c22bcd1cec31de33d6d13f9516d856eead35
Author: Florian Müllner <fmuellner gnome org>
Date:   Sat Jun 22 16:55:08 2019 +0200

    ci: Test building without native backend support
    
    Nobody from the core team tests that configuration, so some non-guarded
    includes regularly sneak in. Avoid those build breakages by adding a
    corresponding job to the CI pipeline.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/637

 .gitlab-ci.yml | 14 ++++++++++++++
 1 file changed, 14 insertions(+)
---
diff --git a/.gitlab-ci.yml b/.gitlab-ci.yml
index a5b576ec2..6387bbf24 100644
--- a/.gitlab-ci.yml
+++ b/.gitlab-ci.yml
@@ -28,6 +28,20 @@ build-mutter:
     - merge_requests
     - /^.*$/
 
+build-without-native-backend:
+  stage: build
+  script:
+    - meson . build -Dbuildtype=debugoptimized -Dnative_backend=false -Dudev=false --werror --prefix /usr
+    - ninja -C build
+    - ninja -C build install
+  artifacts:
+    expire_in: 1 day
+    paths:
+      - build
+  only:
+    - merge_requests
+    - /^.*$/
+
 test-mutter:
   stage: test
   dependencies: