[llvm] [SPIR-V] Fix ldexp exponent splat for vectors wider than four elements (PR #225617)

[Arseniy Obolenskiy via llvm-commits]

aobolensk wrote:

> > HLSL path does not use llvm.ldexp, it uses exp2(Exp) * X:
> > https://github.com/llvm/llvm-project/blob/20913cfb73ee109c0ad4e9cb298e2c1a0595fb0b/clang/include/clang/Basic/HLSLIntrinsics.td#L1118-L1140
> 
> There was suppose to be a pattern match in the PreLegalizer. But im not seeing it right now. llvm/lib/Target/SPIRV/SPIRVCombine.td

Shall we address that? 

https://github.com/llvm/llvm-project/pull/225617