[llvm] [SPIR-V] Add lowering for G_FPOWI (PR #185454)

[Diego Novillo via llvm-commits]

dnovillo wrote:

@Keenuts @s-perron not sure who's an appropriate reviewer for this fix. I'm getting up-to-speed with clang-dxc, so I am looking for focused fixes to help me onboard. I am currently using BigWheels, Vulkan-Samples and the offload test suite as source of things to fix. Glad to take any guidance to where to look next. Thanks.

https://github.com/llvm/llvm-project/pull/185454