Homebrew/homebrew — pull request #28687 by mikemcquaid (2014-04-24 21:34:39+00:00)
Title: build_options: CXX11 is always available on 10.9.

We always have a libc++ there and it's preferential so let's allow the build.cxx11? to always be enabled on Mavericks so we can have e.g. CXX11 bottles where they are useful.

Inspired by #28113.