Add gitlab ci script

This only includes Linux x86_64

.gitlab-ci.yml

+variables:
+  GIT_SUBMODULE_STRATEGY: normal
+
+.core-defs:
+  variables:
+    CORENAME: citra
+    EXTRA_PATH: src/citra_libretro
+    CORE_ARGS: -DENABLE_LIBRETRO=1 -DENABLE_SDL2=0 -DENABLE_QT=0 -DENABLE_WEB_SERVICE=0
+
+.core-linux-defs:
+  extends: .core-defs
+  variables:
+    CORE_ARGS: -DENABLE_LIBRETRO=1 -DLIBRETRO_STATIC=1 -DENABLE_SDL2=0 -DENABLE_QT=0 -DENABLE_WEB_SERVICE=0
+
+include:
+  - template: Jobs/Code-Quality.gitlab-ci.yml
+  - project: 'libretro-infrastructure/ci-templates'
+    file: '/linux-cmake.yml'
+
+stages:
+  - build-prepare
+  - build-shared
+  - test
+
+#Desktop
+libretro-build-linux-x86_64:
+  extends:
+    - .libretro-linux-cmake-x86_64
+    - .core-linux-defs

src/common/CMakeLists.txt

@@ -9,6 +9,9 @@ if ($ENV{CI})
   elseif($ENV{APPVEYOR})
     set(BUILD_REPOSITORY $ENV{APPVEYOR_REPO_NAME})
     set(BUILD_TAG $ENV{APPVEYOR_REPO_TAG_NAME})
+  elseif($ENV{GITLAB_CI})
+    set(BUILD_REPOSITORY $ENV{CI_PROJECT_PATH})
+    set(BUILD_TAG $ENV{CI_COMMIT_TAG})
   endif()
   # regex capture the string nightly or canary into CMAKE_MATCH_1
   string(REGEX MATCH "citra-emu/citra-?(.*)" OUTVAR ${BUILD_REPOSITORY})