Add support for DWP files. http://gcc.gnu.org/wiki/DebugFissionDWP

	Add support for DWP files.  gcc.gnu.org/wiki/DebugFissionDWP
	* contrib/cc-with-tweaks.sh: Add -p parameter to invoke dwp.
	* dwarf2read.c: #include "elf-bfd.h".
	(struct dwarf2_per_objfile): New members dwp_checked, dwp_file.
	(dwop_section_names): Renamed from dwo_section names.  All uses
	updated.  Add entries for .debug_cu_index, .debug_tu_index.
	(struct dwo_file): Rename dwo_name to name, dwo_bfd to dbfd.
	All uses updated.
	(struct dwp_sections): New type.
	(struct virtual_dwo_sections): New type.
	(struct dwp_hash_table): New type.
	(struct dwp_file): New type.
	(init_cutu_and_read_dies): Ensure DWO info/types section has been
	read in.  Handle DWOs coming from DWP files.
	(lookup_dwo_file_slot): New function.
	(dwarf2_locate_dwo_sections): Move definition closer to use.
	(create_dwo_debug_info_hash_table_reader): Renamed from
	create_debug_info_hash_table_reader.  All callers updated.
	(create_dwo_debug_info_hash_table): Renamed from
	create_debug_info_hash_table.  All callers updated.
	(create_dwp_hash_table): New function.
	(locate_virtual_dwo_sections, create_dwo_in_dwp): New functions.
	(lookup_dwo_in_dwp): New function.
	(try_open_dwop_file): Renamed from try_open_dwo_file.  New parameter
	is_dwp.  All callers updated.
	(open_dwop_file): Renamed from open_dwo_file.  All callers updated.
	(open_and_init_dwo_file): Renamed from init_dwo_file.
	All callers updated.
	(lookup_dwo_file): Delete.
	(dwarf2_locate_dwp_sections): New function.
	(hash_dwp_loaded_cutus, eq_dwp_loaded_cutus): New functions.
	(allocate_dwp_loaded_cutus_table): New function.
	(open_and_init_dwp_file): New function.
	(lookup_dwo_cutu): New function.
	(lookup_dwo_comp_unit, lookup_dwo_type_unit): Call it.