[SR-11560] OSS Swift 5.1 does not recognise macCatalyst as a platform.

[Lukasa]

Previous ID	SR-11560
Radar	rdar://problem/68869888
Original Reporter	@Lukasa
Type	Bug

Environment

Swift version 5.1 (swift-5.1-RELEASE)
Target: x86_64-unknown-linux-gnu

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug
Assignee	@devincoughlin
Priority	Medium

md5: b512a39de2bfe46bfd0ebc6402d51081

Issue Description:

If you have an availability annotation that wants to version guard the Catalyst SDK, this triggers warnings when using the OSS version of Swift. This seems like an unnecessary hardship to bear until the next Swift release:

warning: unrecognized platform name 'macCatalyst'
@available(iOS 13.0, macOS 10.15, watchOS 6.0, tvOS 13.0, macCatalyst 13.0, *)

[belkadan]

You don't have to guard Catalyst separately from iOS if they're the same version, but yeah.

[Lukasa]

@swift-ci create

[Lukasa]

This appears to affect subsequent releases as well: Linux 5.2 and 5.3-nightly are also unaware of the macCatalyst platform.

[tshortli]

I believe this was resolved by #29017.