[clang] Correctly compute conversion seq for args to fn with reversed param order (PR #68999)

[Utkarsh Saxena via cfe-commits]

usx95 wrote:

This breaks new code (expected) but does not respect `-Wno-ambiguous-reversed-operator`.  https://godbolt.org/z/oMsGeK1nc
@zygoloid IIUC this should be silenced by this warning but somehow does not. Will investigate further.
Reverting to put out large unsuppresable breakages

https://github.com/llvm/llvm-project/pull/68999