[clang] [llvm] [HLSL] Implement the `reflect` HLSL function (PR #122992)

[Finn Plummer via llvm-commits]

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+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
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+// RUN: %clang_cc1 -O1 -triple spirv-pc-vulkan-compute %s -emit-llvm -o - | FileCheck %s
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inbelic wrote:

Do we also want to test a DirectX target? Or is the purpose of this test just to check we generate the intrinsic rather than expansion.

https://github.com/llvm/llvm-project/pull/122992