[clang] [HLSL] Add ByteAddressBuffer definition to HLSLExternalSemaSource #113477 (PR #116699)

[Helena Kotas via cfe-commits]

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+// RUN: %clang_cc1 -triple dxil-pc-shadermodel6.3-library -x hlsl -emit-llvm -disable-llvm-passes -o - %s | FileCheck %s --check-prefixes=CHECK,CHECK-DXIL
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hekota wrote:

Rename to ByteAddressBuffer**s**-constructor**s**.hlsl - test cases for other byte address buffers will be added here later on. 

https://github.com/llvm/llvm-project/pull/116699