After 40a54c43 (Repair bounds-checking runtime), and in particular
5d648485 (Now btest pass!) `make test` was broken on ARCH != i386,
because I've changed btest to unconditionally run on all arches.
But bounds-checking itsels is only supported on i386 and oops...
Fix it.
Reported-by: Thomas Preud'homme <robotux@celest.fr>