More gdb/skip.c C++ification

More gdb/skip.c C++ification

- Make skiplist_entry a class with private data members.
- Move all construction logic to the ctor.
- Make skip_file_p etc be methods of skiplist_entry.
- Use std::list for the skip entries chain.  Make the list own its
  elements.
- Get rid of the ALL_SKIPLIST_ENTRIES/ALL_SKIPLIST_ENTRIES_SAFE
  macros, use range-for / iterators instead.
- function_name_is_marked_for_skip 'function_sal' argument must be
  non-NULL, so make it a reference instead.

All skiplist_entry invariants are now controlled by skiplist_entry
methods/internals.  Some gdb_asserts disappear for being redundant.

gdb/ChangeLog:
2017-08-11  Pedro Alves  <palves@redhat.com>

	* infrun.c (process_event_stop_test): Adjust
	function_name_is_marked_for_skip call.
	* skip.c: Include <list>.
	(skiplist_entry): Make it a class with private fields, and
	getters/setters.
	(skiplist_entry_chain): Delete.
	(skiplist_entries): New.
	(skiplist_entry_count): Delete.
	(highest_skiplist_entry_num): New.
	(ALL_SKIPLIST_ENTRIES, ALL_SKIPLIST_ENTRIES_SAFE): Delete.
	(add_skiplist_entry): Delete.
	(skiplist_entry::skiplist_entry): New.
	(skiplist_entry::add_entry): New.
	(skip_file_command, skip_function): Adjust.
	(compile_skip_regexp): Delete.
	(skip_command): Don't compile regexp here.  Adjust to use
	skiplist_entry::add_entry.
	(skip_info): Adjust to use range-for and getters.
	(skip_enable_command, skip_disable_command): Adjust to use
	range-for and setters.
	(skip_delete_command): Adjust to use std::list.
	(add_skiplist_entry): Delete.
	(skip_file_p): Delete, refactored as ...
	(skiplist_entry::do_skip_file_p): ... this new method.
	(skip_gfile_p): Delete, refactored as ...
	(skiplist_entry::do_gskip_file_p): ... this new method.
	(skip_function_p, skip_rfunction_p): Delete, refactored as ...
	(skiplist_entry::skip_function_p): ... this new method.
	(function_name_is_marked_for_skip): Now returns bool, and takes
	the function sal by const reference.  Adjust to use range-for and
	skiplist_entry methods.
	(_initialize_step_skip): Remove references to
	skiplist_entry_chain, skiplist_entry_count.
	* skip.h (function_name_is_marked_for_skip): Now returns bool, and
	takes the function sal by const reference.