Fix overflow in ipa_profile_generate_summary

Fix overflow in ipa_profile_generate_summary

With profile count scaling we now get overflow in ipa_profile_generate_summary
which uses old macro GCOV_COMPUTE_SCALE that is not ready for very large
counts.  This patch replaces remaining two uses of it by (somewhat elaborate)
profile-count based equivalent which is overflow safe.

gcc/ChangeLog:

	* basic-block.h (GCOV_COMPUTE_SCALE): Remove.
	* ipa-profile.cc (ipa_profile_generate_summary): Use
	profile-count scaling.
	* sched-rgn.cc (compute_trg_info): Likewise.