macOS Big Sur is version 11 not 11.0

[Ryan Schmidt]

Based on the fact that Apple has released a beta of macOS Big Sur 11.1 already, we can now see that Big Sur should be referred to as version 11, not 11.0 (and it would be reasonable to expect that next year's macOS will be version 12).

If you are fixing any ports that had been coded to assume the macOS version was always 10.x, be sure that you're not fixing it to simply accept versions 10.x or 11.x. Instead, remove any assumption about the version number so that you won't have to revisit the problem again every year.

When Josh released MacPorts 2.6.4 recently, he used the number 11.0 on the Big Sur installer package. For the next version, we should use the version number 11 to denote Big Sur.

I did the same when naming the Big Sur buildbot machines and will change them from 11.0 to 11 soon.

Part of our decision to use "11.0" came from the way that Apple named the SDK: MacOSX11.0.sdk. We will have to see if they change this to MacOSX11.1.sdk in a future version of Xcode and the CLT. If they do, that would represent a change from their previous strategy, and it would be a problem for MacPorts because the SDK path gets baked into some ports. Previously this was ok since the SDK path would stay the same for the life of the OS version, but if it now changes during the life of the OS we may find ourselves needing to rebuild some ports to update their SDK paths.

We may also need to adjust how MacPorts selects the SDK version and SDK path, depending on whether Apple changes the SDK name.