MINIFICPP-1096 appveyor ctest output-on-failure

Signed-off-by: Arpad Boda <aboda@apache.org>

This closes #756
diff --git a/win_build_vs.bat b/win_build_vs.bat
index 2ffef3d..095cb35 100644
--- a/win_build_vs.bat
+++ b/win_build_vs.bat
@@ -79,7 +79,7 @@
 	IF !ERRORLEVEL! NEQ 0 ( popd & exit /b !ERRORLEVEL! )
 )
 if [%skiptests%] NEQ [ON] ( 
-	ctest -C %cmake_build_type%
+	ctest -C %cmake_build_type% --output-on-failure
 	IF !ERRORLEVEL! NEQ 0 ( popd & exit /b !ERRORLEVEL! )
 )
 popd