Update .gitlab-ci.yml to add VS2017 build jobs

use anchors for job definitions

.gitlab-ci.yml

+.VS_64_GENERIC_TEMPLATE: &VS_GENERIC_x64
+  variables:
+    ARCHITECTURE:   "x64"
+  script: "CI\\Windows.bat"
+
+.VS_32_GENERIC_TEMPLATE: &VS_GENERIC_x32
+  variables:
+    ARCHITECTURE:   "x32"
+  script: "CI\\Windows.bat"
+  
+.VS2013_COMMON_TEMPLATE: &VS2013_COMMON
+  variables:
+    BUILD_PLATFORM: "VS2013"
+  tags:
+    - VS2013
+
+.VS2015_COMMON_TEMPLATE: &VS2015_COMMON
+  variables:
+    BUILD_PLATFORM: "VS2015"
+  tags:
+    - VS2015
+
+.VS2017_COMMON_TEMPLATE: &VS2017_COMMON
+  variables:
+    BUILD_PLATFORM: "VS2017"
+  tags:
+    - VS2017
+
 gcc-c++11:
   script: "CI/ci-linux.sh gcc C++11"
   tags:
@@ -21,38 +49,29 @@ cppcheck:
     paths:
       - cppcheck.log
 
+VS2017-64-bit:
+  <<: *VS_GENERIC_x64
+  <<: *VS2017_COMMON
+
+VS2017-32-bit:
+  <<: *VS_GENERIC_x32
+  <<: *VS2017_COMMON
+  
 VS2015-64-bit:
-  variables:
-    BUILD_PLATFORM: "VS2015"
-    ARCHITECTURE:   "x64"
-  script: "CI\\Windows.bat"
-  tags:
-    - VS2015
+  <<: *VS_GENERIC_x64
+  <<: *VS2015_COMMON
 
 VS2015-32-bit:
-  variables:
-    BUILD_PLATFORM: "VS2015"
-    ARCHITECTURE:   "x32"
-  script: "CI\\Windows.bat"
-  tags:
-    - VS2015
-
+  <<: *VS_GENERIC_x32
+  <<: *VS2015_COMMON
 
 VS2013-64-bit:
-  variables:
-    BUILD_PLATFORM: "VS2013"
-    ARCHITECTURE:   "x64"
-  script: "CI\\Windows.bat"
-  tags:
-    - VS2013
+  <<: *VS_GENERIC_x64
+  <<: *VS2013_COMMON
 
 VS2013-32-bit:
-  variables:
-    BUILD_PLATFORM: "VS2013"
-    ARCHITECTURE:   "x32"
-  script: "CI\\Windows.bat"
-  tags:
-    - VS2013
+  <<: *VS_GENERIC_x32
+  <<: *VS2013_COMMON
 
 doc:
   script: "CI/ci-doc.sh"