Fix PR gdb/961.

	Fix PR gdb/961.
	* dwarf2read.c 	(dwarf_ranges_offset, dwarf_ranges_size): New
	variables.
	(RANGES_SECTION): New.
	(dwarf_ranges_buffer): New variable.
	(struct comp_unit_head): Add member "die".
	(struct dwarf2_pinfo): Add dwarf_ranges_buffer, dwarf_ranges_size.
	(DWARF_RANGES_BUFFER, DWARF_RANGES_SIZE): New.
	(dwarf2_has_info): Init dwarf_ranges_offset and dwarf_ranges_size.
	(dwarf2_locate_sections): Likewise.
	(dwarf2_build_psymtabs): Read .debug_ranges.
	(dwarf2_build_psymtabs_hard): Swap dwarf_ranges out.
	(psymtab_to_symtab_1): Swap dwarf_ranges in.  Set cu_header.die.
	(dwarf2_get_pc_bounds): New cu_header argument; adjust all callers.
	Look for DW_AT_ranges and return the bounding box.