portconfigure::choose_supported_archs oddity

[Jeremy Lavergne]

portconfigure::choose_supported_archs iterates down a list of given
architectures, adding them to the return set if found in the
supported_archs list. This makes sense, however it also has a few
confusing lines after this general check.

It also explicitly checks for and adds the 32-bit version of an
unsupported 64-bit architecture (e.g., x86_64 isn't in the list, if i386
is then add it). The 32-bit version will already get visited as the
function iterates across the arch list.

This seems odd; the only way this makes sense if the full set of archs
aren't being checked to begin with.

Have I missed something?