[Foundation] Fallback to presuming 32-bit platforms if we dont explicitly know that it is 64 bit; this allows for better portability

[phausler]

This should resolve rdar://problem/46683060

[phausler]

@swift-ci please smoke test

[itaiferber]

Looks reasonable to me. We'll need to be careful to correctly add 64-bit platforms in the future, but being conservative is good.

[jrose-apple]

This seems like a bad idea to me. Most platforms people are trying to port Swift to are 64-bit these days. #else + #error would be a lot safer.

[itaiferber]

@jrose-apple Is there a more future-proof way to avoid breaking the build?
I don't disagree that being explicit (and aiming for 64-bit) is a good idea, but there are also platforms we can't necessarily know to switch on.

[jrose-apple]

This seems like one of those "trap early" philosophy things: it is better to break the build at the point where something is unknown, with an explicit message, then to stumble on and fail later when you don't know what's missing.

[itaiferber]

@phausler I'll let you make the call here. I'm alright with taking care of this internally too.

[phausler]

@swift-ci please smoke test

[phausler]

I really wish we had a #if bits(64) or #if bits(32) or something like that. It would alleviate this type of error.

[phausler]

@swift-ci please smoke test

[xwu]

@phausler I'm not really in a position to work on it at the moment, but I do have a start on that exact feature here: #14413.