This are internal helper functions; the API functions that use them
already use LONG.

user32: Use a simplified sequence to destroy windows at thread exit, since we don't want to send messages.

winapi_extract: --spec-files has been broken for a long time and does not seem to be useful so remove it.

Using GL_NV_vertex_program2_option so far. If we're really desparate we can
handle some cases without the extension by using a custom varying and texkill
in the fragment program.