[clang] [Sema] Reject unqualified lookup of local nested class name (PR #192678)

[via cfe-commits]

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arrowten wrote:

@zwuis I guess inside the function scope, the lookup process goes through more contexts which accidentally allowed A::B to be seen as B (the reason for passing). The change fixes this by explicitly ignoring names coming from class scopes during such lookups, making the function scope behave correctly too.

https://github.com/llvm/llvm-project/pull/192678