Simplify the detection of a QtSimulator build

We don't need the cumbersome CONFIG+=simulator flag. Now we automatically
build it.

Change-Id: Iab20816856ec1d79965b980a17e668d04d3d9258
Reviewed-by: Rainer Keller <rainer.keller@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>
Avoid blocking simulator backend during its construction

This avoids a race condition when QDeclarativePositionSource::start()
is called before the simulator backend has returned from its eventloop.
The disadvantage is that the first returned set of position data may be
invalid until the initial data set was pushed by the emulator.

Change-Id: I6a8b4330bc50ced154afd2a6248bb0dd3e151c9f
Reviewed-by: Rainer Keller <rainer.keller@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>