sparse: define dummy BUILD_BUG_ON definition for sparse

BUILD_BUG_ON() causes a syntax error to detect coding errors.  So it
causes sparse to detect an error too.  This reduces sparse's usefulness.

This patch makes a dummy BUILD_BUG_ON() definition for sparse.

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Dave Hansen <dave@linux.vnet.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>