[llvm] x86: fix musttail sibcall miscompilation (PR #168956)

[Eli Friedman via llvm-commits]

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efriedma-quic wrote:

On other targets, if IsEligibleForTailCallOptimization concludes a musttail call can't actually be tail-called, we emit an error.  Probably x86 should do this too, so weird edges break loudly instead of miscompiling.

https://github.com/llvm/llvm-project/pull/168956