Further P0135 refinement.

Further P0135 refinement.

	* call.c (build_user_type_conversion_1): Consider conversions from
	a single element in an initializer-list.
	(build_temp): Undo early_elide_copy change.
	(build_over_call): Check that we don't try to copy a TARGET_EXPR
	in C++17 mode.  Set user_conv_p here.
	(convert_like_real): Not here.
	(check_self_delegation): Split out from...
	(build_special_member_call): ...here.  Handle C++17 copy elision.
	* cvt.c (early_elide_copy): Remove.
	(ocp_convert): Undo early_elide_copy change.
	* except.c (build_throw): Likewise.
	* init.c (expand_default_init): Likewise.
	* typeck.c (cp_build_modify_expr): Likewise.

From-SVN: r240889