Report inferior signals as signals, not exceptions, on FreeBSD

Description

Report inferior signals as signals, not exceptions, on FreeBSD

This is the FreeBSD equivalent of r238549.

This serves 2 purposes:

LLDB should handle inferior process signals SIGSEGV/SIGILL/SIGBUS/ SIGFPE the way it is suppose to be handled. Prior to this fix these signals will neither create a coredump, nor exit from the debugger or work for signal handling scenario.

eInvalidCrashReason need not report "unknown crash reason" if we have a valid si_signo