for some inexplicable reason, configure.bat went into an endless loop
on win 8.1+ while attempting to parse the command line; this is clearly
a bug in cmd, so work around it.

amends 7af6e9bb

.

Task-number: QTBUG-58019
Change-Id: I698a2a51891a4e7af75836c075888f70df865409
Reviewed-by: Jake Petroules <jake.petroules@qt.io>