Gcc: Upstream Patch

The accepted upstream patch is mildly different to the one we currently ship for Yosemite, most notably because the upstream patch doesn’t touch libsanitizer.
Patch is failing to apply so you can probably just use the gist version of this patch and remove the change log bits that don't apply: http://bot.brew.sh/job/Homebrew%20Pull%20Requests/15682/version=mavericks/testReport/junit/brew-test-bot/mavericks/install_gcc/