[llvm] [AArch64][GlobalISel] Improve lowering of vector fp16 fptrunc (PR #163398)

[Ryan Cowan via llvm-commits]

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HolyMolyCowMan wrote:

I had to make these changes to get the tests to pass, I agree it would be best not to have to make them but adding a new opcode changed the values.

https://github.com/llvm/llvm-project/pull/163398