add MSVC 2017 to github actions

Author: andreasbuhr

.github/workflows/cmake.yml

@@ -38,6 +38,12 @@ jobs:
             cxx_flags: -stdlib=libc++,
             exe_linker_flags: -lc++,
           }
+          - {
+            name: "Windows MSVC 2017 (x64)",
+            os: windows-2016,
+            cxx: "cl",
+            environment_script: "C:/Program Files (x86)/Microsoft Visual Studio/2017/Enterprise/VC/Auxiliary/Build/vcvars64.bat",
+          }
           - {
             name: "Windows MSVC 2019 (x64)",
             os: windows-latest,