[llvm] [LV] Teach the loop vectorizer llvm.sincos is trivially vectorizable (PR #128035)

[Benjamin Maxwell via llvm-commits]

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MacDue wrote:

I've added a simple predicated test case. The cost is the same (for the actual intrinsics) -- however, the LV only deems it worth vectorizable when the vector library is available this time (which seems reasonable). 

https://github.com/llvm/llvm-project/pull/128035