Use libiberty hash in gas/symbols.c.

Use libiberty hash in gas/symbols.c.

	* symbols.c (struct symbol_entry): New.
	(hash_symbol_entry): Likewise.
	(eq_symbol_entry): Likewise.
	(symbol_entry_alloc): Likewise.
	(symbol_entry_find): Likewise.
	(local_symbol_make): Use htab hash table.
	(local_symbol_convert): Likewise.
	(symbol_table_insert): Likewise.
	(symbol_find_exact_noref): Likewise.
	(resolve_local_symbol): Likewise.
	(resolve_local_symbol_values): Likewise.
	(symbol_begin): Likewise.
	(symbol_print_statistics): Likewise.