[gdb/symtab] Add gdb/dwarf2/error.h

Add a new header file gdb/dwarf2/error.h, containing macros:
- DWARF_ERROR, and
- DWARF_ERROR_PREFIX.

The DWARF_ERROR_PREFIX is to be used in dwarf errors in a follow-up patch.

No functional changes.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>

gdb/dwarf2/error.h

@@ -0,0 +1,29 @@
+/* DWARF error handling utilities.
+
+   Copyright (C) 2024 Free Software Foundation, Inc.
+
+   This file is part of GDB.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 3 of the License, or
+   (at your option) any later version.
+
+   This program is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+   GNU General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program.  If not, see <http://www.gnu.org/licenses/>.  */
+
+#ifndef GDB_DWARF2_ERROR_H
+#define GDB_DWARF2_ERROR_H
+
+/* Canonical capitalization of "dwarf error".  */
+#define DWARF_ERROR "Dwarf Error"
+
+/* Prefix to be used in dwarf errors.  */
+#define DWARF_ERROR_PREFIX DWARF_ERROR ": "
+
+#endif /* GDB_DWARF2_ERROR_H */