We build "Supporting Files" out of QMAKE_INTERNAL_INCLUDED_FILES, which
is really not supposed to be exposed to the user like that, but since
the variable will hold user-included pri files eg., the Xcode generator
piggy-backs on this variable to list the files.
To make the project view in Xcode a bit cleaner we explicitly exclude
any file living inside the Qt directory, meaning we won't show all the
pri and prf files from Qt's mkspecs directory anymore.
Change-Id: I828700aceac5fdf3ea2b27d9ba3885543c2ad137
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@digia.com>