[gdb] Add tsan-suppressions.txt

Add a new file tsan-suppressions.txt, to suppress the "unlock unlocked mutex"
problem in ncurses, filed in PR29328.

The file is added to the TSAN_OPTIONS in lib/gdb.exp.

Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=29328

---
 gdb/testsuite/lib/gdb.exp |  9 +++++++++
 gdb/tsan-suppressions.txt | 18 ++++++++++++++++++
 2 files changed, 27 insertions(+)

diff --git a/gdb/testsuite/lib/gdb.exp b/gdb/testsuite/lib/gdb.exp
index a29b8f947c4..49b00391729 100644
--- a/gdb/testsuite/lib/gdb.exp
+++ b/gdb/testsuite/lib/gdb.exp
@@ -32,6 +32,15 @@ if {$tool == ""} {
 # (which will affect any spawned sub-process) to avoid this.
 append ::env(ASAN_OPTIONS) ",detect_leaks=0"
 
+set tsan_suppressions suppressions=$srcdir/../tsan-suppressions.txt
+if { ![info exists env(TSAN_OPTIONS) ]
+     || $env(TSAN_OPTIONS) == "" } {
+    set env(TSAN_OPTIONS) "$tsan_suppressions"
+} else {
+    append env(TSAN_OPTIONS) ":$tsan_suppressions"
+}
+unset tsan_suppressions
+
 # List of procs to run in gdb_finish.
 set gdb_finish_hooks [list]
 
diff --git a/gdb/tsan-suppressions.txt b/gdb/tsan-suppressions.txt
new file mode 100644
index 00000000000..5f1e5dc7ea7
--- /dev/null
+++ b/gdb/tsan-suppressions.txt
@@ -0,0 +1,18 @@
+# Copyright (C) 2022 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/>.
+
+# Problem in ncurses, see:
+# - https://sourceware.org/bugzilla/show_bug.cgi?id=29328.
+# - https://lists.gnu.org/archive/html/bug-ncurses/2022-07/msg00002.html
+mutex:newterm