* dwarf2read.c (MAX_CACHE_AGE): Lower to 5.

	* dwarf2read.c (MAX_CACHE_AGE): Lower to 5.
	(struct dwarf2_cu): Add dependencies and mark fields.
	(free_one_comp_unit): New function, broken out from
	free_comp_units_worker.
	(dwarf2_add_dependence, dwarf2_clear_marks, dwarf2_mark)
	(dwarf2_mark_helper): New functions.
	(psymtab_to_symtab_1): Call free_one_comp_unit.  Re-enable
	aging.
	(read_full_die): Call dwarf2_add_dependence.
	(free_comp_units_worker): Call free_one_comp_unit.  Use
	marking to free old comp units.