PR c++/31388
	* cp-tree.h (ARITHMETIC_TYPE): Include COMPLEX_TYPE.
	* typeck.c (type_after_usual_arithmetic_conversions): Adjust, as
	COMPLEX_TYPE is now an ARITHMETIC_TYPE.
	* init.c (build_zero_init): Adjust, as
	COMPLEX_TYPE is now a SCALAR_TYPE.
	* typeck2.c (digest_init): Allow brace-enclosed initializers for
	COMPLEX_TYPE, even though that is now a SCALAR_TYPE.

	PR c++/31388
	* g++.dg/ext/complex2.C: New test.

From-SVN: r124172