To build the VM you need: git, cmake, wget, gnu-tar, the latest version of Xcode, and the MacOSX 10.6 SDK.
One way of downloading and installing these is to use the homebrew package manager:
# install homebrew with the following oneliner:
ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
# if you haven't installed git yet
brew install git
# if you haven't installed cmake yet
brew install cmake
# wget is needed in certain cases to download files
brew install wget
# OSX' default tar doesn't feature 7z compression needed for for some 3rd party libs
#Follow the instruction of `brew info gnu-tar` to make this `tar` version the system default
brew install gnu-tar --default-names
Install the latest version of XCode and XCode command line tools. Download MacOSX10.6.sdk.zip and put in Xcode SDK folder:
# make sure you're root: sudo su
cd /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs
wget http://files.pharo.org/vm/src/lib/MacOSX10.6.sdk.zip
unzip MacOSX10.6.sdk.zip
rm MacOSX10.6.sdk.zip