Taken from http://bugzilla.kernel.org/show_bug.cgi?id=11567

If you even define KBUILD_EXTRA_SYMBOLS in Makefile it will not be expanded
into command line argument for modpost.
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>