Deduplicate require_running macros and move them up

Deduplicate require_running macros and move them up

I find it very confusing to define the require_running in the middle of
the file, and re-define it to something else later in the middle of the
same file.  I think it would be better if those macros had different
names so that we know exactly what they do.

gdb/gdbserver/ChangeLog:

	* server.c (require_running): Rename to ...
	(require_running_or_return): ... this ...
	(require_running_or_break): ... and this.
	(handle_query, process_serial_event): Adjust.