Change get_std_name_hint to use generated hash table

The get_std_name_hint function so far uses linear search to locate
matching entries.  After adding more hint entries this might not be
appropriate anymore.  Therefore this patch also replaces the linear
array with a gperf-generated hash table.

contrib/ChangeLog

	* gcc_update (files_and_dependencies): Add rule for
	gcc/cp/std-name-hint.h.

gcc/cp/ChangeLog

	* Make-lang.in: Add rule to rebuild std-name-hint.h from
	std-name-hint.gperf.
	* name-lookup.cc (get_std_name_hint): Remove hints array.
	Use gperf-generated class std_name_hint_lookup.
	Include "std-name-hint.h".
	* std-name-hint.gperf: New file.
	* std-name-hint.h: New file.  Generated from the .gperf file.