C requires prototypes or compilers will complain about them missing. Our
library entry points do not have such, therefore add the macro
FREERDP_ENTRY_POINT which declares the function prototype automatically
before the function.
This is the contemporary way of including find modules and including the
find module this way avoids cmake errors in conjunction with
find_package_handle_standard_args().
Signed-off-by: Kimon Hoffmann <Kimon.Hoffmann@lawo.com>
