ci/windows: add back build-error detection
This was accidentally broken while refactoring the script.
Fixes: bf3c772e ("ci: Improve vs2019 mesa_build.ps1 for remove the need of cmd.exe")
This was accidentally broken while refactoring the script.
Fixes: bf3c772e ("ci: Improve vs2019 mesa_build.ps1 for remove the need of cmd.exe")