build: Warn when using snapshot on Armv6
build: Warn when using snapshot on Armv6

Building io.js on armv6 with snapshot enabled does not work due to a bug in v8,
so it now warns when building on armv6 and having snapshot enabled.

PR-URL: https://github.com/iojs/io.js/pull/282
Reviewed-By: Rod Vagg <f9f03903429036ef609ed7ca822fddfa76155c29@vagg.org>

dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node,dreamllq/node