re PR c/79515 (ICE: tree check: expected class 'type', have 'exceptional' (error_mark) in do_warn_double_promotion, at c-family/c-warn.c:1867)

	PR c/79515
	* c-warn.c (do_warn_double_promotion): Don't warn if an invalid
	conversion has occured.

	* gcc.dg/dfp/pr79515.c: New.

From-SVN: r245485