[SR-15801] compiler crash "there should be no duplicate decls" while building swift-corelibs-foundation

[QuietMisdreavus]

Previous ID	SR-15801
Radar	rdar://problem/88299954
Original Reporter	@QuietMisdreavus
Type	Bug

Environment

Swift snapshot, current main branch

Additional Detail from JIRA

Votes	0
Component/s	swift
Labels	Bug
Assignee	@QuietMisdreavus
Priority	Medium

md5: 541cf6968fe028b7f3806cb651d9d69f

Issue Description:

https://ci.swift.org/job/swift-corelibs-foundation-PR-macOS/2804/console

This is an issue caused by rdar://87601741 (PR 40860) - getDisplayDecls is collecting more decls, and adds an assertion that it shouldn't collect duplicates. This was added to prevent loading a module's underlying Clang module repeatedly, but it looks like it's also being hit for separate Clang modules, due to decls that ClangImporter automatically adds, such as __NSConstantString. This is causing compilation failures in corelibs-foundation's CI.

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@swift-ci create

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#41115