See the [annoucement](http://www.mruby.org/releases/2014/11/19/mruby-1.1.0-released.html).
Prior to this we tried to use pre-built LLVM binaries since Yosemite, but starting with Rubinius 2.3.0 this is no longer a feature of its build system. Instead, look for "llvm" Homebrew package and suggest installing it if it's missing.
http://www.jruby.org/2014/12/09/jruby-1-7-17 Highlights: 56 issues fixed for 1.7.17 native crypt() Fixed bad encoding of string interpolated within backticks popen2+ now works properly with env hash improvements to align MRI and JRuby FFI updated stdlib to 1.9.3p392 (+ rexml security fixes) tzdata updated
Rubinius fails to download a prebuilt LLVM on Yosemite since one is not available yet. Instead, download the prebuilt version for the previous OS X release. This fixes Rubinius 2.2.7+ builds, but the older ones still fail for me on Yosemite. This could be due to the fact that they're old releases which are not compatible with never dependencies on the system.
Rubinius never supported the `--with-libyaml-dir` configure option, so we can never use `--if needs_yaml` since it's incompatible and might break the build if libyaml was auto-discovered from Homebrew. Starting from 2.2.0, Rubinius doesn't even need libyaml anymore since it stopped building psych. Instead it requires users to install psych as a gem which vendors its own libyaml anyway.