Problems:
1. linking -dl lib on FreeBSD platform
2. backtrace from ld-elf shows r_debug_state() instead of _dl_debug_state()

Cause:
1. There is no dl library on FreeBSD platform test has to ignore linking "-ldl"
2. The stop due to a shared library event shows backtrace frame #0
function as r_debug_state()

Test passed:
PASS: gdb.base/break-probes.exp: set stop-on-solib-events 1

gdb/ChangeLog:
2018-04-20  Rajendra SY  <rajendra.sy@gmail.com>

        PR gdb/23095
        * gdb/testsuite/gdb.base/break-probes.exp: