build_homebrew.sh builds a homebrew OSX build, but doesn't upload it

This allows me to keep track of when the Homebrew build breaks
Set JULIA_CPU_TARGET=core2

@ihnorton should we be doing this on windows as well?  See https://github.com/JuliaLang/julia/issues/5459 and https://groups.google.com/forum/#!msg/julia-users/xK8iE2nwc_4/Ki2MJyTAE0wJ