build: check before removing %config% link

PR-URL: #51437
Reviewed-By: Vinícius Lourenço Claro Cardoso <contact@viniciusl.com.br>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>

vcbuild.bat

@@ -337,7 +337,8 @@ if errorlevel 1 (
 if "%target%" == "Clean" goto exit
 
 :after-build
-rd %config%
+:: Check existence of %config% before removing it.
+if exist %config% rd %config%
 if errorlevel 1 echo "Old build output exists at 'out\%config%'. Please remove." & exit /B
 :: Use /J because /D (symlink) requires special permissions.
 if EXIST out\%config% mklink /J %config% out\%config%