I don't use Mac much myself, so I don't know the versions...
But if you have lldb then I recommend to use it. lldb+fpdebug was introduced in Lazarus 2.0 and has been proven stable since. (at least as stable as the gdb solution).
If not, well you need to supply more on the gdb issue (the actual gdb output / the crashed dlg may have a "more" button? or before doing F9, open menu View > ide internals > debug output ).
But if indeed gdb itself crashed, then there is little that can be done.
If you build it yourself, maybe build without assertions (in case it failed on an assertion, and I have seen cases, were the assertion were wrong, then again I don't know if the code after the assertion would have dealt withe the data...)
In any case if there are issues, you can try different debug info settings. Either dwarf-2 or dwarf-3. Dwarf 2 is probably less likely to upset gdb.