This was used by Rubinius over the years to ensure that a correct llvm version was selected from the ones available on the system, but for recent Rubinius this function is a no-op, and since Rubinius isn't an actively maintained project anymore, I don't feel strongly for keeping ruby-build workarounds that only help ancient Rubinius versions.
Internally, ruby-build will want to set `--with-openssl-dir` if we try
to detect Homebrew's OpenSSL or build one for the OS X. However,
Rubinius doesn't support that configure flag. So, this translates
`--with-openssl-dir` to a combination of `--with-lib-dir` and
`--with-include-dir`.