c++: Fix base copy elision thinko [PR98744]

As Jakub points out in the PR, I was mixing up
DECL_HAS_IN_CHARGE_PARM_P (which is true for the abstract maybe-in-charge
constructor) and DECL_HAS_VTT_PARM_P (which is true for a base constructor
that needs to handle virtual bases).

gcc/cp/ChangeLog:

	PR c++/98744
	* call.c (make_base_init_ok): Use DECL_HAS_VTT_PARM_P.

gcc/testsuite/ChangeLog:

	PR c++/98744
	* g++.dg/init/elide7.C: New test.