buildsym API cleanup

buildsym API cleanup

gdb/ChangeLog:

	* buildsym.c (buildsym_objfile): New static global.
	(buildsym_comp_dir): New static global.
	(finish_block_internal): Delete arg objfile.  All callers updated.
	(finish_block): Delete arg objfile.  All callers updated.
	(start_subfile): Delete arg dirname.  All callers updated.
	(patch_subfile_names): Update buildsym_comp_dir.
	(get_macro_table): Delete arg objfile.  All callers updated.
	(start_symtab): New arg objfile.  All callers updated.
	Rename arg dirname to comp_dir.
	(reset_symtab_globals): Initialize buildsym_objfile, buildsym_comp_dir.
	(end_symtab_get_static_block): Delete arg objfile.  All callers
	updated.
	(end_symtab_without_blockvector): Ditto.
	(end_symtab_with_blockvector): Ditto.
	(end_symtab_from_static_block): Ditto.
	(end_symtab): Ditto.
	(end_expandable_symtab): Ditto.
	(augment_type_symtab): Ditto.
	* coffread.c (coff_start_symtab): New arg objfile.  All callers
	updated.