re PR middle-end/46674 (Weak alias is mistakenly optimized away)

re PR middle-end/46674 (Weak alias is mistakenly optimized away)

	PR middle-end/46674
	PR middle-end/46221
	* varasm.c (symbol_alias_set_t): New typedef for derived pointer_set
	wrapper class.
	(symbol_alias_set_create): New wrapper function.
	(symbol_alias_set_destroy): Likewise.
	(symbol_alias_set_contains): Likewise.
	(symbol_alias_set_insert): Likewise.
	(compute_visible_aliases): Use the above and return symbol_alias_set_t,
	not a pointer_set.
	(remove_unreachable_alias_pairs): Adjust likewise to match.
	(finish_aliases_1): Likewise.

From-SVN: r168047