[NFC][HLSL] Move emitter out of AMDGPU.cpp

- Create a home for LangBuiltins
- Move all HLSL code out of AMDGPU.cpp to CGHLSLBuiltins.cpp

Author: farzonl

.github/new-prs-labeler.yml

@@ -637,6 +637,7 @@ hlsl:
   - clang/lib/Sema/HLSLExternalSemaSource.cpp
   - clang/lib/Sema/SemaHLSL.cpp
   - clang/lib/CodeGen/CGHLSLRuntime.*
+  - clang/lib/CodeGen/LangBuiltins/CGHLSLBuiltins.cpp
   - llvm/include/llvm/Frontend/HLSL/**
   - llvm/lib/Frontend/HLSL/**
 

clang/lib/CodeGen/CMakeLists.txt

@@ -115,6 +115,7 @@ add_clang_library(clangCodeGen
   PatternInit.cpp
   SanitizerMetadata.cpp
   SwiftCallingConv.cpp
+  LangBuiltins/CGHLSLBuiltins.cpp
   TargetBuiltins/ARM.cpp
   TargetBuiltins/AMDGPU.cpp
   TargetBuiltins/Hexagon.cpp