Fix integer overflow in profile_count::probability_in

Fix integer overflow in profile_count::probability_in

This patch fixes integer overflow in profile_count::probability_in which happens
for very large counts.  This was probably not that common in practice until
scaled AutoFDO profiles were intorduces.

This was introduced as cut&paste from profile_probability implementation.
I reviewed multiplicaitons in the file for safety and noticed that in some
cases the code is over-protective. In profile_probability::operator/ we alrady
scale that m_val <= other.m_val and thus we know result will be in the range
0...max_probability.  In profile_probability::apply_scale we deal with 30bit
value from profile_probability so no overflow can happen.

gcc/ChangeLog:

	* profile-count.h (profile_probability::operator/): Do not cap
	twice.
	(profile_probability::operator/=): Likewise.
	(profile_probability::apply_scale): Do not watch for overflow.
	(profile_count::probability_in): Watch overflow.