Fixed test case to compile & run on FreeBSD

Fixed test case to compile & run on FreeBSD

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()

gdb/ChangeLog:

	PR gdb/23095
	* gdb/testsuite/gdb.base/break-probes.exp: Pass shlib_load to
	prepare_for_testing.  Set normal_bp to r_debug_state if target
	is bsd.