valops.c: Overload resolution code: Rename parameters/locals

valops.c: Overload resolution code: Rename parameters/locals

While looking over this code, I thought the names of the parameters to
find_oload_champ and related functions and locals were a bit too
cryptic.  For example, FN_LIST holds methods, not free functions.
Free-functions are in OLOAD_SYMS.

This patch renames parameters/variables to the more obvious
methods/xmethods/functions instead.

gdb/ChangeLog:
2018-11-21  Pedro Alves  <palves@redhat.com>

	* valops.c (find_method_list, value_find_oload_method_list)
	(find_overload_match, find_oload_champ): Rename parameters and
	locals.