Re-enable ios_exception_minidump_generator being built on non-ARM.

This file gets built on x86 as part of building Chromium for the iOS simulator,
which I had forgotten in the course of https://breakpad.appspot.com/664002/.

R=mark@chromium.org

Review URL: https://breakpad.appspot.com/774002

git-svn-id: http://google-breakpad.googlecode.com/svn/trunk@1238 4c0a9323-5329-0410-9bdc-e9ce6186880e