Mac: make platformsupport a static lib

Mac: make platformsupport a static lib

The "force framework/no-framework" logic does not
really work, since Qt is now a mix of frameworks
and statics libs. Remove this code path and use
the "detection" path instead.

Also remove the exports from platformsupport.

Change-Id: I0a308666480445eb47c4f443ff7529addecad10d
Reviewed-on: http://codereview.qt.nokia.com/3464
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@nokia.com>
Reviewed-by: Morten Johan Sørvig <morten.sorvig@nokia.com>