portindex: spoof compiler version

[mohd-akram]

Fixes: https://trac.macports.org/ticket/71755

Versions from https://gist.github.com/yamaya/2924292

[jmroot]

We don't want to do this all the time, but only in pretend mode. This is also only one factor that can affect the output. If we're going to go down this path, I'd like to see a general mechanism for overriding variables, with the policy of what to set them to left to the caller.

[mohd-akram]

We don't want to do this all the time, but only in pretend mode.

Currently the code is checking port_options to only do this in pretend mode.

This is also only one factor that can affect the output.

What are some others?

If we're going to go down this path, I'd like to see a general mechanism for overriding variables, with the policy of what to set them to left to the caller.

Within the scope of this PR or in the future? Do you mean the caller should specify the compiler version? I refrained from that because the caller would have to have knowledge of which Xcode version is supported on which macOS version, and which compiler comes with that Xcode. portindex is also called from a shell script, so the user has no easy access to the MacPorts API to aid with information like this.