ada: Suppress warning about Subprogram_Variant failing at run time

ada: Suppress warning about Subprogram_Variant failing at run time

Warning about check failing at run time is likely spurious for mutually
recursive subprograms with multiple variant clauses. These will be
non-trivial to detect, so we simply suppress the warning altogether for
all subprogram variants.

gcc/ada/

	* exp_prag.adb (Expand_Pragma_Check): Suppress warning for checks of
	subprogram variants.