Apply clang fix for assertion building llvm with libc++ 15

Apply clang fix for assertion building llvm with libc++ 15

Merge commit f1b0a4fc540f from llvm git (by Richard Smith):

  An expression should only contain an unexpanded parameter pack if it
  lexically contains a mention of the pack.

  Systematically distinguish between syntactic and semantic references to
  packs, especially when propagating dependence from a type into an
  expression. We should consult the type-as-written when computing
  syntactic dependence and should consult the semantic type when computing
  semantic dependence.

  Fixes #54402.

MFC after:	3 days