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I used MacPorts to install all the required compilers, libraries and such, this file lists all of the packages I have installed: installed_ports_osx_10.11.1.txt. Installing MacPorts will require installing the XCode command line tools, but that is explained on the MacPorts page.
You can use this script to install these ports:
I had to put in two extra symlinks because there were places where the name of the compiler seemed to either be hardwired, or where using envvars to specify the compiler messed up other parts of the build process.
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