[libcxx-commits] [libcxx] [libc++] Fix ambiguity in ranges::advance and ranges::next affecting flat_set (PR #177773)

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halbi2 wrote:

This modifies `ranges::advance` but does not test the modifications to `ranges::advance`, only a new test case in `flat_set` which is not related to `advance`.

https://github.com/llvm/llvm-project/pull/177773