qtest: kill orphaned qtest QEMU processes on FreeBSD

On Linux we use PR_SET_PDEATHSIG to kill orphaned QEMU processes
if we fail to call qtest_quit(), or the test program aborts/segvs.
This prevents meson from hanging forever due to the orphaned
process keeping stdout open.

On FreeBSD we can achieve the same using PROC_PDEATHSIG_CTL, which
gives us the equivalent protection against hangs.

Signed-off-by: "Daniel P. Berrangé" <berrange@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20230912184130.3056054-3-berrange@redhat.com>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230914155422.426639-6-alex.bennee@linaro.org>

tests/qtest/libqtest.c

@@ -24,6 +24,9 @@
 #ifdef __linux__
 #include <sys/prctl.h>
 #endif /* __linux__ */
+#ifdef __FreeBSD__
+#include <sys/procctl.h>
+#endif /* __FreeBSD__ */
 
 #include "libqtest.h"
 #include "libqmp.h"
@@ -414,6 +417,10 @@ static QTestState *G_GNUC_PRINTF(1, 2) qtest_spawn_qemu(const char *fmt, ...)
          */
         prctl(PR_SET_PDEATHSIG, SIGKILL, 0, 0, 0);
 #endif /* __linux__ */
+#ifdef __FreeBSD__
+        int sig = SIGKILL;
+        procctl(P_PID, getpid(), PROC_PDEATHSIG_CTL, &sig);
+#endif /* __FreeBSD__ */
         if (!g_setenv("QEMU_AUDIO_DRV", "none", true)) {
             exit(1);
         }