Preserve Android deployment target in Swift module filenames

[somiljain2006]

Fixes #1167

Preserve deployment target in Android module filenames. Android module filenames must retain the deployment target because it is part of the target triple used for module lookup. Other platforms continue to use the unversioned triple. Adds a regression test covering Android, Apple, and Linux triples.

[jakepetroules]

Why hasn't this surfaced as an issue so far?

[somiljain2006]

My understanding is that this is a fairly specific code path. The existing behavior is correct on Apple platforms, and the issue only manifests on Android, where the API level is encoded in the target triple used for module lookup. That likely limits the number of users affected.

[jakepetroules]

#1167 was filed some time ago. Are you actually still seeing this issue with nightly?

This change doesn't seem correct, unless someone is actively making changes recently to change the behavior. @finagolfin are you aware of anything that has changed the swiftmodule naming scheme on Android lately?

[finagolfin]

My guess is the linked issue was back when Android support wasn't done yet in this new build system back in March, but ever since Jake and Owen added that support in the next month, I have not seen a single issue related to Android versioning, and we now have several repos building with versioned target triples for Android.

I suggest that these users try the latest 6.4 snapshot and report any issues they see with some detailed build output. I did just make a change in trunk today, swiftlang/swift#90650, but that shouldn't affect anyone and these reports long predate that anyway.