Speed up CI build by avoiding vcvarsalls.bat (#1484)

.github/workflows/main.yml

@@ -51,18 +51,18 @@ jobs:
       PLATFORM: ${{ matrix.config.platform }}
 
     steps:
+      - name: Environment
+        run: |
+          echo "C:\\Program Files (x86)\\Microsoft Visual Studio\\${{matrix.config.vs}}\\Enterprise\\MSBuild\\Current\\Bin" | Out-File -FilePath $env:GITHUB_PATH -Encoding utf8 -Append
       - uses: actions/checkout@v2
-
       - name: Setup
         shell: cmd
         run: |
-          call "C:\Program Files (x86)\Microsoft Visual Studio\%VS_VERSION%\Enterprise\VC\Auxiliary\Build\vcvarsall.bat" %PLATFORM%
           build\premake5.exe --file=build\scripts\LLVM.lua download_llvm --arch=%PLATFORM%
 
       - name: Build
         shell: cmd
         run: |
-          call "C:\Program Files (x86)\Microsoft Visual Studio\%VS_VERSION%\Enterprise\VC\Auxiliary\Build\vcvarsall.bat" %PLATFORM%
           build\premake5.exe --file=build\premake5.lua vs%VS_VERSION% --arch=%PLATFORM%
           msbuild build\vs%VS_VERSION%\CppSharp.sln /p:Configuration=Release /verbosity:minimal
 

build/scripts/LLVM.lua

@@ -56,16 +56,34 @@ function get_vs_version()
   local function map_msvc_to_vs_version(major, minor)
     if major == "19" and minor >= "20" then return "vs2019"
     elseif major == "19" and minor >= "10" then return "vs2017"
-    elseif major == "19" then return "vs2015"
-    elseif major == "18" then return "vs2013"
-    elseif major == "17" then return "vs2012"
-    else error("Unknown MSVC compiler version, run in VS command prompt.") end
+    end
+  end
+
+  local function map_msbuild_to_vs_version(major, minor)
+    if major == "16" then return "vs2019"
+    elseif major == "15" then return "vs2017"
+	end
+  end
+
+  local out = outputof("cl")  
+  local major, minor = string.match(out, '(%d+).(%d+).%d+.?%d*%s+')  
+  local version = map_msvc_to_vs_version(major, minor)
+  if version ~= nil then
+    return version
+  end
+
+  out = outputof("msbuild -version -nologo")
+  major, minor = string.match(out, '(%d+).(%d+).') 
+  version = map_msbuild_to_vs_version(major, minor)
+  if version ~= nil then
+    return version
   end
 
-  local out = outputof("cl")
-  local major, minor = string.match(out, '(%d+).(%d+).%d+.?%d*%s+')
-  
-  return map_msvc_to_vs_version(major, minor)
+  if major ~= nil then
+    error("Unsupported MSVC compiler version.") 
+  else
+    error("Unknown MSVC compiler version, run in VS command prompt.")
+  end
 end
 
 function get_toolset_configuration_name(arch)