mingw: add check for artifact on github releases

Author: rainers

windows/build_mingw.bat

@@ -3,11 +3,13 @@
 set ROOT=%CD%
 mkdir "%ROOT%\artifacts"
 
-set ARTIFACT=mingw-libs-%MINGW_VER%-2.zip
+set TAG=mingw-libs-%MINGW_VER%-2
+set ARTIFACT=%TAG%.zip
 set ARTIFACTPATH=%ROOT%\artifacts\%ARTIFACT%
+set GITHUB_RELEASE=https://github.com/dlang/installer/releases/download/%TAG%/%ARTIFACT%
 
 REM Stop early if the artifact already exists
-powershell -Command "Invoke-WebRequest downloads.dlang.org/other/%ARTIFACT% -OutFile %ARTIFACTPATH%" && exit /B 0
+powershell -Command "Invoke-WebRequest %GITHUB_RELEASE% -OutFile %ARTIFACTPATH%" && exit /B 0
 
 set DMD_URL=http://downloads.dlang.org/releases/2.x/%D_VERSION%/dmd.%D_VERSION%.windows.7z
 echo DMD_URL=%DMD_URL%