For the windows file system engine, we add an extra macro to use
library loading if configured to do so, but avoid it on WinRT, as
none of the symbols would be found.
We also QT_REQUIRE_CONFIG(library) in the library headers and
exclude the sources from the build if library loading is disabled.
This, in turn, makes it necessary to clean up some header inclusions.
Change-Id: I2b152cb5b47a2658996b6f4702b038536a5704ec
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@qt.io>
d6330a19b2