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
#You also need to install the xz decompression tool that will be used by tar
brew install xz
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