c++: DR2303, ambiguous base deduction [PR97453]

c++: DR2303, ambiguous base deduction [PR97453]

When there are two possible matches and one is a base of the other, choose
the derived class rather than fail.

gcc/cp/ChangeLog

2020-10-21  Kamlesh Kumar  <kamleshbhalui@gmail.com>
	    Jason Merrill  <jason@redhat.com>

	PR c++/97453
	DR2303
	* pt.c (get_template_base): Consider closest base in template
	deduction when base of base also matches.

gcc/testsuite/ChangeLog

2020-10-21  Kamlesh Kumar  <kamleshbhalui@gmail.com>

	* g++.dg/DRs/dr2303.C: New test.