[gdb/testsuite] Add gdb.dwarf2/clang-debug-names.c

Add test-case with .debug_names section using DW_FORM_ref4.

There's currently no support for .debug_names in the dwarf assembler, so we
use plain _emit rather than something more structured.

Consequently, we cannot use regular declare_labels-generated labels to refer
from .debug_names to .debug_info.  Instead, we use labels with a
predefined name, which we generate using _compute_label, and then define using
define_label.

This is the test-case for PR25952, so kfail the corresponding test.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-05-08  Tom de Vries  <tdevries@suse.de>

	* gdb.dwarf2/clang-debug-names.c: New test.
	* gdb.dwarf2/clang-debug-names.exp: New file.

1 files changed, 25 insertions, 0 deletions

diff --git a/gdb/testsuite/gdb.dwarf2/clang-debug-names.c b/gdb/testsuite/gdb.dwarf2/clang-debug-names.c
new file mode 100644
index 0000000..d66c192
--- /dev/null
+++ b/gdb/testsuite/gdb.dwarf2/clang-debug-names.c
@@ -0,0 +1,25 @@
+/* This testcase is part of GDB, the GNU debugger.
+
+   Copyright 2020 Free Software Foundation, Inc.
+
+   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/>.  */
+
+int
+main (void)
+{
+  asm ("main_label: .globl main_label");
+  int sum, a, b;
+  sum = a + b;
+  return sum;
+}