c++: 'new T[N]' and SFINAE [PR82110]

c++: 'new T[N]' and SFINAE [PR82110]

Here we're failing to treat 'new T[N]' as erroneous in a SFINAE context
when T isn't default constructible because expand_aggr_init_1 doesn't
communicate to build_aggr_init (its only SFINAE caller) whether the
initialization was actually successful.  To fix this, this patch makes
expand_aggr_init_1 and its subroutine expand_default_init return true on
success, false on failure so that build_aggr_init can properly return
error_mark_node on failure.

	PR c++/82110

gcc/cp/ChangeLog:

	* init.c (build_aggr_init): Return error_mark_node if
	expand_aggr_init_1 returns false.
	(expand_default_init): Change return type to bool.  Return false
	on error, true on success.
	(expand_aggr_init_1): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp0x/pr78765.C: Expect another conversion failure
	diagnostic.
	* g++.dg/template/sfinae14.C: Flip incorrect assertion.
	* g++.dg/cpp2a/concepts-requires27.C: New test.