Merge branch 'ci' into 'master'

CI: added debian, macos, win32 and win64 build jobs.

See merge request !2

.gitlab-ci.yml

+stages:
+    - build
+
+build-debian:
+    image: registry.videolan.org:5000/vlc-debian-unstable:20181128113529
+    stage: build
+    tags:
+        - debian
+        - amd64
+    script:
+        - ./bootstrap
+        - mkdir build
+        - cd build
+        - ../configure
+        - make -j $(getconf _NPROCESSORS_ONLN)
+
+build-macos:
+    stage: build
+    tags:
+        - macos
+    script:
+        - ./bootstrap
+        - mkdir build
+        - cd build
+        - ../configure
+        - make -j $(getconf _NPROCESSORS_ONLN)
+
+build-win64:
+    image: registry.videolan.org:5000/vlc-debian-win64:20181107154313
+    stage: build
+    tags:
+        - debian
+        - amd64
+        - win64
+    script:
+        - ./bootstrap
+        - mkdir build
+        - cd build
+        - ../configure --host=x86_64-w64-mingw32
+        - make -j $(getconf _NPROCESSORS_ONLN)
+
+build-win32:
+    image: registry.videolan.org:5000/vlc-debian-win32:20181107151708
+    stage: build
+    tags:
+        - debian
+        - amd64
+        - win32
+    script:
+        - ./bootstrap
+        - mkdir build
+        - cd build
+        - ../configure --host=i686-w64-mingw32
+        - make -j $(getconf _NPROCESSORS_ONLN)