MIPS/testsuite: Include stdio.h in mipscop tests

gcc/testsuite

	* gcc.c-torture/compile/mipscop-1.c: Include stdio.h.
	* gcc.c-torture/compile/mipscop-2.c: Ditto.
	* gcc.c-torture/compile/mipscop-3.c: Ditto.
	* gcc.c-torture/compile/mipscop-4.c: Ditto.