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

[Joseph Huber via cfe-commits]

================
@@ -0,0 +1,71 @@
+//===---- __clang_gpu_builtin_vars.h - GPU built-in variables --------------===
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===-----------------------------------------------------------------------===
+
+#ifndef __CLANG_GPU_BUILTIN_VARS_H__
+#define __CLANG_GPU_BUILTIN_VARS_H__
+
+#if defined(__HIP__) || defined(__CUDA__)
+
+#include <gpuintrin.h>
+
+// The warpSize is a runtime value rather than a compile-time constant.
+inline __attribute__((device)) const struct {
+  __attribute__((device, always_inline, const)) operator int() const noexcept {
+    return __gpu_num_lanes();
+  }
+} warpSize{};
+
+// Make sure nobody can create instances of the coordinate types, take their
+// address, copy, or assign them.
+#pragma push_macro("__GPU_DISALLOW_BUILTINVAR_ACCESS")
+#define __GPU_DISALLOW_BUILTINVAR_ACCESS(__tag)                                \
+  __attribute__((device)) __tag() = delete;                                    \
+  __attribute__((device)) __tag(const __tag &) = delete;                       \
+  __attribute__((device)) void operator=(const __tag &) const = delete;        \
+  __attribute__((device)) __tag *operator&() const = delete
+
+#pragma push_macro("__GPU_COORD_BUILTIN")
+#define __GPU_COORD_BUILTIN(__tag, __fx, __fy, __fz)                           \
+  struct __tag {                                                               \
+    __declspec(property(get = __get_x)) unsigned int x;                        \
+    __declspec(property(get = __get_y)) unsigned int y;                        \
+    __declspec(property(get = __get_z)) unsigned int z;                        \
+    __attribute__((device, always_inline)) unsigned int __get_x() const {      \
+      return __fx;                                                             \
+    }                                                                          \
+    __attribute__((device, always_inline)) unsigned int __get_y() const {      \
+      return __fy;                                                             \
+    }                                                                          \
+    __attribute__((device, always_inline)) unsigned int __get_z() const {      \
+      return __fz;                                                             \
----------------
jhuber6 wrote:

They're struct members so I actually wasn't sure if they needed it. I'll double check.

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