Set CU BASE_ADDRESS already from partial DIEs.

	Set CU BASE_ADDRESS already from partial DIEs.
	* dwarf2read.c (read_partial_die): New variables BASE_ADDRESS and
	BASE_ADDRESS_TYPE.  Set these variables from DW_AT_LOW_PC and
	DW_AT_ENTRY_PC.  Set CU->HEADER.BASE_KNOWN and CU->HEADER.BASE_ADDRESS
	from these variables if it was still unset.