[clang] [Clang][HIP] Add LLVM vendored device headers for `*-llvm` triple (PR #203980)

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``````````bash
git-clang-format --diff origin/main HEAD --extensions cpp,h,c -- clang/lib/Headers/__clang_gpu_builtin_vars.h clang/lib/Headers/__clang_gpu_device_functions.h clang/lib/Headers/__clang_gpu_intrinsics.h clang/test/Headers/gpu-device-functions.cpp clang/lib/Driver/ToolChains/HIPAMD.cpp clang/lib/Frontend/InitPreprocessor.cpp clang/test/Preprocessor/predefined-macros.c --diff_from_common_commit
``````````

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``````````diff
diff --git a/clang/lib/Headers/__clang_gpu_builtin_vars.h b/clang/lib/Headers/__clang_gpu_builtin_vars.h
index c14cf82ca..01e9b637d 100644
--- a/clang/lib/Headers/__clang_gpu_builtin_vars.h
+++ b/clang/lib/Headers/__clang_gpu_builtin_vars.h
@@ -61,7 +61,8 @@ __GPU_COORD_BUILTIN(__gpu_builtin_gridDim_t, __gpu_num_blocks_x(),
 #pragma pop_macro("__GPU_COORD_BUILTIN")
 #pragma pop_macro("__GPU_DISALLOW_BUILTINVAR_ACCESS")
 
-static inline const __attribute__((device)) __gpu_builtin_threadIdx_t threadIdx{};
+static inline const
+    __attribute__((device)) __gpu_builtin_threadIdx_t threadIdx{};
 static inline const __attribute__((device)) __gpu_builtin_blockIdx_t blockIdx{};
 static inline const __attribute__((device)) __gpu_builtin_blockDim_t blockDim{};
 static inline const __attribute__((device)) __gpu_builtin_gridDim_t gridDim{};

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https://github.com/llvm/llvm-project/pull/203980