btrace: check for indirect jump return in _Unwind_RaiseException

Some versions of _Unwind_RaiseException, e.g. on Fedora 28, use an
indirect jump to return to the exception handler.

This messes up the output of "record function-call-history /c" since the
return is interpreted as cross-function goto.  It had been detected by
gdb.btrace/exception.exp.

Add a heuristic for "_Unwind_*" functions to interpret an indirect jump
that ends in one of our caller functions as return to the first instance
of that function in our call stack.

gdb/
	* btrace.c (ftrace_update_function): Add indirect jump heuristic.