ipa/100308 - properly update the callgraph when pruning EH in IPA CP

ipa/100308 - properly update the callgraph when pruning EH in IPA CP

This makes sure to fall into the delete_unreachable_blocks_update_callgraph
handling to remove blocks becoming unreachable when removing EH edges
by tracking blocks to need EH cleanup and doing that after releasing
dominance info.

This fixes an ICE seen with gfortran.dg/gomp/pr88933.f90 when enhancing
DSE.

2021-04-28  Richard Biener  <rguenther@suse.de>

	PR ipa/100308
	* ipa-prop.c (ipcp_modif_dom_walker::before_dom_children):
	Track blocks to cleanup EH in new m_need_eh_cleanup.
	(ipcp_modif_dom_walker::cleanup_eh): New.
	(ipcp_transform_function): Release dominator info before
	doing EH cleanup.