c++: Fix ({ ... }) array mem-initializer.

Here, we were going down the wrong path in perform_member_init because of
the incorrect parens around the mem-initializer for the array.  And then
cxx_eval_vec_init_1 didn't know what to do with a CONSTRUCTOR as the
initializer.  For GCC 9, let's just fix the latter issue.

gcc/cp/ChangeLog
2020-03-02  Jason Merrill  <jason@redhat.com>

	PR c++/86917
	* constexpr.c (cxx_eval_vec_init_1): Handle CONSTRUCTOR.

3 files changed