View -> Debug windows -> Call Stack
The Call Stack window lists the names and line numbers of the most recent end of the call "chain" that brought you to the point of the crash.
If there is no debug or line number info for called code, you won't get line numbers, of course. Much of the FPC code does not ship with debug info, so unless you recompile those parts to include debug info you will not be able to use to the debugger to trace meaningfully into such FPC code.
However, usually SIGSEGV faults are down to errors in your code, not to bugs in RTL or LCL libraries.