Fix system test backtrace generation on OpenBSD

On Linux core dump contains absolute path to crashed binary

    Core was generated by `/home/newman/isc/ws/bind9/bin/named/.libs/lt-named -D glue-ns1 -X named.lock -m'.

However, on OpenBSD there's only a basename

    Core was generated by `named'.

This commit adds support for the latter, retains the former.

bin/tests/system/run.sh.in

@@ -265,7 +265,10 @@ if [ -n "$core_dumps" ]; then
         export SYSTESTDIR="$systest"
         echoinfo "D:$systest:backtrace from $coredump:"
         echoinfo "D:$systest:--------------------------------------------------------------------------------"
-        binary=$(gdb --batch --core="$coredump" 2>/dev/null | sed -ne "s/Core was generated by \`//;s/ .*'.$//p;")
+        binary=$(gdb --batch --core="$coredump" 2>/dev/null | sed -ne "s|Core was generated by \`\([^' ]*\)[' ].*|\1|p")
+        if [ ! -f "${binary}" ]; then
+            binary=$(find "${top_builddir}" -path "*/.libs/${binary}" -type f)
+        fi
         "${top_builddir}/libtool" --mode=execute gdb \
                                   -batch \
                                   -ex bt \