ARM: 6140/1: silence a bogus sparse warning in unwind.c

The check for compiler which is supposed to miscompile unwind tables
clearly has nothing to do with sparse (which does not define necessary
macros anyway), so simply silence it.

Signed-off-by: Alexander Shishkin <virtuoso@slind.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>