gcc compilers to be supported by Macports, especially on older MacOS systems

[Chris Jones]

> OOTH: If gcc10 is available and installed, why would you want to call in a full build of gcc13 unnecessarily to build the port?

If you are suggesting the builds should check to see what the user has 
installed and pick a compiler based on that, then no, absolutely not. 
That is just introducing non-reproducibility into the builds which we 
should never do. The builds should be the same on anyone's machine (and 
the buildbots) regardless of whatever compilers the user happened to 
have installed to start with.

The best way to ensure the minimum set of compilers get installed on 
anyones machine is for all port builds to follow the same basic rules on 
picking a compiler, which is what the current system does. It picks the 
most recent available for a given system that isn't blacklisted by the 
port in question. I see no reason to change this, and certainly not to 
intentionally introduce non-reproducibility into out builds.

Chris