[Development] Remember to rebuild qmake in dev

[Oswald Buddenhagen]

On Thu, Jul 21, 2016 at 09:27:58AM -0700, Thiago Macieira wrote:
> moc.prf with MSVC now depends on a side feature in qmake to help support 
> generating the moc_predefs.h file. If you're using MSVC, please remember to 
> recompile qmake soon.
> 
a much better recommendation is "run config.status (or configure -redo
on windows) *every time* after pulling". this ensures that qmake is
rebuilt, and possible adjustments to the configuration are done.
it takes about half a minute (soon much quicker, as we're about to
finally add chaching), and if nothing actually changes, it won't have
any impact on the subsequent rebuild.

this requirement certainly seems a bit arbitrary, but it's an inevitable
consequence of the qmake bootstrapping.