Add sem_item::m_hash_set (PR ipa/78309)

Add sem_item::m_hash_set (PR ipa/78309)

	PR ipa/78309
	* ipa-icf.c (void sem_item::set_hash): Update m_hash_set.
	(sem_function::get_hash): Use the new field.
	(sem_function::parse): Remove an argument from ctor.
	(sem_variable::parse): Likewise.
	(sem_variable::get_hash): Use the new field.
	(sem_item_optimizer::read_section): Use new ctor and set hash.
	* ipa-icf.h: _hash is removed from sem_item::sem_item,
	sem_variable::sem_variable, sem_function::sem_function.

From-SVN: r242687