Update build-windows-toolchain.bat

Report errors properly

Author: compnerd

utils/build-windows-toolchain.bat

@@ -83,6 +83,9 @@ powershell.exe -ExecutionPolicy RemoteSigned -File %~dp0build.ps1 ^
   %TestArg% ^
   -Stage %StagePath%
 
+:: Fail if powershell.exe exited with error code 1 or above (failure)
+if ErrorLevel 1 exit /b 1
+
 :: Clean up the module cache
 rd /s /q %LocalAppData%\clang\ModuleCache