[SYCL][NFC] Add copyright header to the library sources

Signed-off-by: Alexey Bader <[email protected]>

Author: bader

sycl/source/detail/posix_pi.cpp

@@ -1,3 +1,11 @@
+//==---------------- posix_pi.cpp ------------------------------------------==//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
 #include <CL/sycl/detail/defines.hpp>
 
 #include <dlfcn.h>

sycl/source/detail/windows_pi.cpp

@@ -1,3 +1,11 @@
+//==---------------- windows_pi.cpp ----------------------------------------==//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
 #include <CL/sycl/detail/defines.hpp>
 
 #include <windows.h>