Dump the backtrace to stdout when core is found in systest directory

bin/tests/system/run.gdb

@@ -0,0 +1 @@
+thread apply all bt full

bin/tests/system/run.sh

@@ -195,6 +195,18 @@ else
         echoinfo "I:$systest:Test claims success despite crashes: $core_dumps"
         echofail "R:$systest:FAIL"
         # Do not clean up - we need the evidence.
+	find "$systest/" -name 'core*' | while read -r coredump; do
+		SYSTESTDIR="$systest"
+		echoinfo "D:$systest:backtrace from $coredump start"
+		binary=$(gdb --batch --core="$coredump" | sed -ne "s/Core was generated by \`//;s/ .*'.$//p;")
+		"$TOP/libtool" --mode=execute gdb \
+			       --batch \
+			       --command=run.gdb \
+			       --core="$coredump" \
+			       -- \
+			       "$binary"
+		echoinfo "D:$systest:backtrace from $coredump end"
+	done
     elif [ $assertion_failures -ne 0 ]; then
         echoinfo "I:$systest:Test claims success despite $assertion_failures assertion failure(s)"
         echofail "R:$systest:FAIL"