For ".pragma library" there is a special flag in QmlJS::Directives.
We just need to actually set the flag and query it when re-emitting the
code.
Change-Id: Ia3455fda18aba3219b02ecf092bb28987a6ccef5
Fixes: QTCREATORBUG-22326
Reviewed-by: Thomas Hartmann <thomas.hartmann@qt.io>