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: nodejs#282
Reviewed-By: Rod Vagg <rod@vagg.org>

configure

@@ -944,4 +944,8 @@ else:
 
 gyp_args += args
 
+#print warning when snapshot is enabled and building on armv6
+if (is_arch_armv6()) and (not options.without_snapshot):
+  print '\033[1;33mWarning!! When building on ARMv6 use --without-snapshot\033[1;m'
+
 sys.exit(subprocess.call(gyp_args))