Fix 'nmake qch_docs' failed on Windows
Fix 'nmake qch_docs' failed on Windows

Task-number: QTBUG-24953

Change-Id: I949e724f718603f58a163351499b639c631a2d80
Reviewed-by: Casper van Donderen <808524cef5c654648bea2a2b954f3b3445ed083c@nokia.com>

kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc,kobolabs/qtdoc