[clang] [libcxx] Reapply "[Clang] Implement resolution for CWG1835 (#92957, #98547)" (PR #100425)

[Krystian Stasiowski via cfe-commits]

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@@ -767,6 +757,7 @@ bool Sema::BuildCXXNestedNameSpecifier(Scope *S, NestedNameSpecInfo &IdInfo,
   else
     Diag(IdInfo.IdentifierLoc, diag::err_undeclared_var_use)
         << IdInfo.Identifier;
+#endif
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sdkrystian wrote:

Yeah, these changes shouldn't really be part of this PR. Just something I noticed when refactoring `BuildCXXNestedNameSpecifier` that needs to go. I'll address it in another PR.

https://github.com/llvm/llvm-project/pull/100425