Kbuild, lto, workaround: Don't warn for initcall_reference in modpost

This reference is discarded, but can cause warnings when it refers to
exit. Ignore for now.

This is a workaround and can be removed once we get rid of
-fno-toplevel-reorder

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Link: http://lkml.kernel.org/r/1391846481-31491-7-git-send-email-ak@linux.intel.com
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>