This adds rudimentary support for linking against xcframeworks. We can
now do
LIBS += /absolute/path/to/some.xcframework
and this will end up in the frameworks section of the Xcode project.
This is required for linking against the FFmpeg xcframeworks we're
providing for iOS.
Pick-to: 6.8 6.9
Task-number: QTBUG-86387
Task-number: QTBUG-129651
Change-Id: Id212700d3554689160d23eafb26d99ac43b91062
Reviewed-by: Alexandru Croitor <alexandru.croitor@qt.io>
1185f651e3