Add many methods to buildsym_compunit

Add many methods to buildsym_compunit

This adds many methods to buildsym_compunit and makes the data members
private.  Essentially the entire buildsym API is now available as a
method on buildsym_compunit.  However, standalone functions are still
provided, as this is what the sybmol readers actually use.

gdb/ChangeLog
2018-07-20  Tom Tromey  <tom@tromey.com>

	* buildsym.c (buildsym_compunit::buildsym_compunit): Do more
	initialization.
	(buildsym_compunit): Add new constructor.
	(struct buildsym_compunit) <get_last_source_file, finish_block,
	record_block_range, start_subfile, patch_subfile_names,
	push_subfile, pop_subfile, record_line, get_compunit_symtab,
	set_last_source_start_addr, get_last_source_start_addr,
	get_local_using_directives, set_local_using_directives,
	get_global_using_directives, outermost_context_p,
	get_current_context_stack, get_context_stack_depth,
	get_current_subfile, get_local_symbols, get_file_symbols,
	get_global_symbols, record_debugformat, record_producer,
	push_context, pop_context, end_symtab_get_static_block,
	end_symtab_from_static_block, end_symtab, end_expandable_symtab>:
	New public methods.
	<record_pending_block, finish_block_internal, make_blockvector,
	watch_main_source_file_lossage, end_symtab_with_blockvector>: New
	private methods.
	Update all users.