configure.bat / qt-configure-module.bat fail with arguments containing equal signs

Arguments like -DCMAKE_PREFIX_PATH=something end up split in the config.opt file that is read by QtProcessConfigureArgs.cmake.

This happens, because we're writing the arguments in a loop:

for %%a in (%*) do (
    echo %%a >> config.opt
)

and this treats the equal sign as argument separator, leading to the following config.opt content:

-DCMAKE_PREFIX_PATH
something