[llvm] [SPIR-V] Select int-to-int convert opcode from source signedness (PR #201116)

[Viktoria Maximova via llvm-commits]

https://github.com/vmaksimo commented:

should not we also change `llvm/test/CodeGen/SPIRV/transcoding/OpenCL/convert_functions.ll`?

https://github.com/llvm/llvm-project/pull/201116