configure: use __ARM_ARCH to determine arm version

Before this change, configure used processor specific macro defines
(like __ARM_ARCH_6M__) to detect the arm processor version. This
changes configure to use __ARM_ARCH, that should be defined to the
correct version.

Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
PR-URL: https://github.com/nodejs/node/pull/4123