[SR-9252] Source compatibility failure in Tagged project (master branch)

[xedin]

Previous ID	SR-9252
Radar	None
Original Reporter	@xedin
Type	Bug

Additional Detail from JIRA

Votes	0
Component/s	Compiler, Standard Library
Labels	Bug, SourceCompatibility
Assignee	None
Priority	Medium

md5: 32737c25a375811c27bc118d623e45c1

Issue Description:

After adding AdditiveArithmetic protocol one of the source compatibility suite projects `Tagged` started failing with following error:

/Users/buildnode/jenkins/workspace-private/swift-master-source-compat-suite/project_cache/Tagged/Sources/Tagged/Tagged.swift:110:1: error: conditional conformance of type 'Tagged<Tag, RawValue>' to protocol 'Numeric' does not imply conformance to inherited protocol 'AdditiveArithmetic'
extension Tagged: Numeric where RawValue: Numeric {
^

e.g. https://ci.swift.org/view/Source%20Compatibility/job/swift-master-source-compat-suite/2852/artifact/swift-source-compat-suite/FAIL_Tagged_4.1_BuildSwiftPackage.log

[belkadan]

cc @airspeedswift