ipa-cp: New debug counters for IPA-CP

ipa-cp: New debug counters for IPA-CP

Martin Liška has been asking me to add debug counters to the IPA-CP pass so
that testcase reductions are easier.  The pass already has one for the bit
value propagation, so this patch adds one for value_range propagation
and one for the actual constant propagation.

gcc/ChangeLog:

2020-10-30  Martin Jambor  <mjambor@suse.cz>

	* dbgcnt.def (ipa_cp_values): New counter.
	(ipa_cp_vr): Likewise.
	* ipa-cp.c (decide_about_value): Check and bump ipa_cp_values debug
	counter.
	(decide_whether_version_node): Likewise.
	(ipcp_store_vr_results):Check and bump ipa_cp_vr debug counter.