c++: cleanup ctor_omit_inherited_parms [PR97268]

c++: cleanup ctor_omit_inherited_parms [PR97268]

ctor_omit_inherited_parms was being somewhat abused.  What I'd missed
is that it checks for a base-dtor name, before proceeding with the
check.  But we ended up passing it that during cloning before we'd
completed the cloning.  It was also using DECL_ORIGIN to get to the
in-charge ctor, but we sometimes zap DECL_ABSTRACT_ORIGIN, and it ends
up processing the incoming function -- which happens to work.  so,
this breaks out a predicate that expects to get the incharge ctor, and
will tell you whether its base ctor will need to omit the parms.  We
call that directly during cloning.

Then the original fn is essentially just a wrapper, but uses
DECL_CLONED_FUNCTION to get to the in-charge ctor.  That uncovered
abuse in add_method, which was happily passing TEMPLATE_DECLs to it.
Let's not do that.  add_method itself contained a loop mostly
containing an 'if (nomatch) continue' idiom, except for a final 'if
(match) {...}'  check, which itself contained instances of the former
idiom.  I refactored that to use the former idiom throughout.  In
doing that I found a place where we'd issue an error, but then not
actually reject the new member.

	gcc/cp/
	* cp-tree.h (base_ctor_omit_inherited_parms): Declare.
	* class.c (add_method): Refactor main loop, only pass fns to
	ctor_omit_inherited_parms.
	(build_cdtor_clones): Rename bool parms.
	(clone_cdtor): Call base_ctor_omit_inherited_parms.
	* method.c (base_ctor_omit_inherited_parms): New, broken out of
	...
	(ctor_omit_inherited_parms): ... here, call it with
	DECL_CLONED_FUNCTION.
	gcc/testsuite/
	* g++.dg/inherit/pr97268.C: New.