Install gcc 4.7.2
The "native" gcc on your Mac is quite old. We need to use a new version 4.7.2. Get this version from MacPorts with (in a terminal window),

sudo port install gcc47
You will need to give your password to do this action.

Now, you must configure your Mac to use this gcc 4.7.2 by default. If you don't use your Mac for native development, then you can simply make this change and leave it that way. If you do native development, it's quite easy to switch back and forth between gcc 4.7.2 and the native llvm-gcc 4.2.

To make gcc 4.7.2 your system default, do

sudo port select --set gcc mp-gcc47
To go back to your native gcc (only necessary if you do native Mac development), do

sudo port select --set gcc llvm-gcc42
You can check your gcc version with,

gcc -v
You should see a message at the end like,

gcc version 4.7.2 (MacPorts gcc47 4.7.2_2)
If you get an error, try closing your terminal window and opening a new one.

-------------------------------------------
Install getopt
If you want to use gm2d build or buildtool to build code, you need to update your getopt tool on your Mac (the native Mac version is different than the linux version - here we'll get a version that mimics the linux one). It's easy to undo this step, so there's little risk.

Do...

sudo port install getopt
To uninstall later, just replace install with uninstall and the Mac native getopt will be the default.

----------------------------------------