Sometimes the cselib_record_sp_cfa_base_equiv makes it into the var-tracking
used VALUEs and needs to be preserved.

2020-04-11  Jakub Jelinek  <jakub@redhat.com>

	PR debug/94495
	PR target/94551
	* cselib.c (cselib_record_sp_cfa_base_equiv): Set PRESERVED_VALUE_P on
	val->val_rtx.