Disable precision timers when running MSVC2012 code on pre-Windows 8.

Precision timers can cause the event loop to lock up
when running MSVC2012 code on pre-Windows 8.

Task-number: QTBUG-27266

Change-Id: Idd73731e82843d0d140859bab825bc1a54eccf1a
Reviewed-by: Gunnar Sletta <gunnar.sletta@digia.com>
(cherry picked from qtbase/aa1b4c0943187d82e0c313b93559e99226a9c75a)