scripts/lsan_suppressions.txt: Add more leaks

Running "make check" with the clang leak sanitizer reveals some
leak reports which are either not our problem or else not
a leak which is worth our time to fix. Add some suppressions
for these.

While we're touching the file, add the usual SPDX header
and a comment explaining how to use it.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20260302092225.4088227-3-peter.maydell@linaro.org

scripts/lsan_suppressions.txt

@@ -1,5 +1,26 @@
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+# This is a set of suppressions for LeakSanitizer; you can use it by setting
+#   LSAN_OPTIONS="suppressions=/path/to/scripts/lsan_suppressions.txt"
+# when running a QEMU built with the leak-sanitizer.
+
 # The tcmalloc on Fedora37 confuses things
 leak:/lib64/libtcmalloc_minimal.so.4
 
 # libxkbcommon also leaks in qemu-keymap
 leak:/lib64/libxkbcommon.so.0
+
+# g_set_user_dirs() deliberately leaks the previous cached g_get_user_*
+# values. This is documented in upstream glib's valgrind-format
+# suppression file:
+# https://github.com/GNOME/glib/blob/main/tools/glib.supp
+# This avoids false positive leak reports for the qga-ssh-test.
+leak:g_set_user_dirs
+
+# qemu_irq_intercept_in is only used by the qtest harness, and
+# its API inherently involves a leak.
+# While we could keep track of the old IRQ data structure
+# in order to free it, it doesn't seem very important to fix
+# since it is only used by the qtest test harness.
+# Just ignore the leak, at least for the moment.
+leak:qemu_irq_intercept_in