re PR debug/49382 (-O2 -g: DW_AT_location at the very first PC is already modified)

re PR debug/49382 (-O2 -g: DW_AT_location at the very first PC is already modified)

	PR debug/49382
	* dwarf2out.c (dw_loc_list_node): Add force field.
	(add_var_loc_to_decl): For PARM_DECL, attempt to keep
	the incoming location in the list, even if it is modified
	before first real insn.
	(output_loc_list): Emit empty ranges with force flag set.
	(dw_loc_list): If first range of a PARM_DECL is empty,
	set force flag.

From-SVN: r175076