PR c++/90938 - Initializing array with {1} works, but not {0}

gcc/cp/ChangeLog:

	PR c++/90938
	* tree.c (type_initializer_zero_p): Fail for structs initialized
	with non-structs.

gcc/testsuite/ChangeLog:

	PR c++/90938
	* g++.dg/init/array55.C: New test.
	* g++.dg/init/array56.C: New test.
	* g++.dg/cpp2a/nontype-class33.C: New test.