[llvm] [SYCL] Add libsycl, a SYCL RT library implementation project (PR #144372)

[Kseniya Tikhomirova via llvm-commits]

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@@ -0,0 +1,64 @@
+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+///
+/// \file
+/// This file contains the declaration of the macros defining attributes for
+/// exported methods and defining API namespaces.
+///
+//===----------------------------------------------------------------------===//
+
+#ifndef __LIBSYCL_DETAIL_CONFIG_HPP
+#define __LIBSYCL_DETAIL_CONFIG_HPP
+
+#include <sycl/version.hpp>
+
+#define __LIBSYCL_BEGIN_UNVERSIONED_NAMESPACE namespace sycl {
+#define __LIBSYCL_END_UNVERSIONED_NAMESPACE }
+
+#define __LIBSYCL_BEGIN_VERSIONED_NAMESPACE                                    \
+  __LIBSYCL_BEGIN_UNVERSIONED_NAMESPACE inline namespace __LIBSYCL_ABI_NAMESPACE {
+#define __LIBSYCL_END_VERSIONED_NAMESPACE                                      \
+  }                                                                            \
+  __LIBSYCL_END_UNVERSIONED_NAMESPACE
+
+#ifndef __SYCL_DEVICE_ONLY__
+#ifndef __LIBSYCL_EXPORT
+#ifdef _WIN32
+
+#define __LIBSYCL_DLL_LOCAL
+
+#if __LIBSYCL_BUILD_SYCL_DLL
+#define __LIBSYCL_EXPORT __declspec(dllexport)
+#define __LIBSYCL_EXPORT_DEPRECATED(x) __declspec(dllexport, deprecated(x))
+#else
+#define __LIBSYCL_EXPORT __declspec(dllimport)
+#define __LIBSYCL_EXPORT_DEPRECATED(x) __declspec(dllimport, deprecated(x))
+#endif //__LIBSYCL_BUILD_SYCL_DLL
+
+#else // _WIN32
+
+#define __LIBSYCL_DLL_LOCAL __attribute__((visibility("hidden")))
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KseniyaTikhomirova wrote:

I don't think so. Both versions have gnu specific view `(__attribute__((visibility("hidden")))` vs `[[gnu::visibility("hidden")]]`). It looks like both versions are used among llvm-project subprojects. By any chance do you know if there is any preference?

AFAIK `visibility `and `__visibility__` are both valid. 

https://github.com/llvm/llvm-project/pull/144372