This reduces unnecessary OS conditions in qmake since these platforms
are mutually exclusive, and also opens up their potential for use on
macOS to transparently support multi-arch builds like UIKit platforms.
This is also more similar to what Xcode does, as the DEPLOYMENT_TARGET
variables are platform specific, while the ARCHS variable is not.
DEPLOYMENT_TARGET has a use case for being OS specific in qmake (host
tools vs targets), while ARCHS does not.
Change-Id: Icee838a39e84259c2089faff08cc11d5f849758d
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
603628b1ea