Two issues with stack overflow protection

[Eli Zaretskii]

The implementation of stack_overflow on sysdep.c was recently changed
so as not to use sys/resource.h and getrlimit, but configure.ac still
insists on these two features in order to include the recovery code,
which I think should be fixed.

More importantly, the recovery simply longjmps to command_loop,
whereas similar features like Fthrow and Fsignal do much more in
unwind_to_catch.  Shouldn't stack overflow recovery do that as well?
Otherwise, the specpdl stack, byte_stack_list, lisp_eval_depth
etc. all stay at their values they had at stack overflow time, no?