lib: fix missing FFI imports in gtk3_4

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
lib: fix extern type of NativeFile

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg-s: all extern type use the C structures of kernel::Pointer

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>
nitg-s: fix importation of custom C header between modules

Signed-off-by: Alexis Laferrière <alexis.laf@xymus.net>