Minor testsuite fixes for targets with 16-bit ints and targets without I/O.

Minor testsuite fixes for targets with 16-bit ints and targets without I/O.

	* execute/970312-1.c, execute/980605-1.c (f): Change printf to sprintf.
	* execute/bf-sign-2.c (struct X): Add u15 field.
	(main): Add check for u15.  Conditionalize u31 check depending on
	whether ints are <32 bits or >=32 bits.

From-SVN: r25730