[llvm] [MIPS][ISel] Fix musttail (PR #161860)

[Djordje Todorovic via llvm-commits]

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djtodoro wrote:

@jrtc27 yep, it does make sense to still check it. I incorporated in the new commit (basically - do not check for the optional mips flag for enabling tail calls in case of `musttial`, and I also enabled tail call opts for `dso_local` functions (`1dcb9110612ab`) ). Thanks for the review!

https://github.com/llvm/llvm-project/pull/161860