x86: Detect stack protector for i386 builds on x86_64

Stack protector support was not detected when building with
ARCH=i386 on x86_64 systems:

  arch/x86/Makefile:80: stack protector enabled but no compiler support

The "-m32" argument needs to be passed to the detection script.

Signed-off-by: Michal Schmidt <mschmidt@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Arjan van de Ven <arjan@infradead.org>
LKML-Reference: <20090829182718.10f566b1@leela>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
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