Fix min_flags handling in mod-ref

Fix min_flags handling in mod-ref

gcc/ChangeLog:

2021-08-11  Jan Hubicka  <hubicka@ucw.cz>
	    Alexandre Oliva  <oliva@adacore.com>

	* ipa-modref.c (modref_lattice::dump): Fix escape_point's min_flags
	dumping.
	(modref_lattice::merge_deref): Fix handling of indirect scape points.
	(update_escape_summary_1): Likewise.
	(update_escape_summary): Likewise.
	(ipa_merge_modref_summary_after_inlining): Likewise.

gcc/testsuite/ChangeLog:

	* c-c++-common/modref-dse.c: New test.

(cherry picked from commit 9851a1631f2915fafdc733539b6c8b5fb81e7ae5)