[clang] [HLSL] Implement the `lit` intrinsic (PR #134171)

[Kaitlin Peng via cfe-commits]

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+// NOTE: Assertions have been autogenerated by utils/update_cc_test_checks.py UTC_ARGS: --version 5
+// RUN: %clang_cc1 -finclude-default-header -x hlsl -triple dxil-pc-shadermodel6.3-library %s -fnative-half-type -emit-llvm -O1 -o - | FileCheck %s
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kmpeng wrote:

Just for future reference, when do we want to use `-O1` and/or `-disable-llvm-passes` in tests? I haven't been able to figure out a consistent rule looking through the other codegen tests.

https://github.com/llvm/llvm-project/pull/134171