For now, don't strip `--HEAD` from `ARGV` prior to forking for install.
Currently this doesn't work because the formula object the installer is acting
on has its `prefix` set while under the influence of `--HEAD`. So, the
installer bails out when it sees that nothing is installed to `f.prefix`.
This is a hotfix for issue Homebrew/homebrew#8668 to allow formulae to keep building. A proper
fix should ensure that formula installers are operating on objects with
appropriately set `prefix` values.
39b3ed3c33