[AIE][LIBC] Temporary fix for errno declaration on AIE

Current libc allows to configure the definition of errno, but not its declaration.
The declaration always adds thread_local, which isn't supported on AIE.
A recent upstream commit introduced proper support for configuring errno. Until then, we add guards for AIE.

libc/include/errno.h.def

@@ -4,6 +4,8 @@
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
+// Modifications (c) Copyright 2024 Advanced Micro Devices, Inc. or its affiliates
+//
 //===----------------------------------------------------------------------===//
 
 #ifndef LLVM_LIBC_ERRNO_H
@@ -47,7 +49,11 @@
 
 #ifdef __cplusplus
 extern "C" {
+#ifdef __AIECC__
+extern int __llvmlibc_errno;
+#else
 extern thread_local int __llvmlibc_errno;
+#endif
 }
 #else
 extern _Thread_local int __llvmlibc_errno;