The test reports bogus failures because the loop variable i is declared
as int, and the constant expected in the dump doesn't fit in an int for avr.
Fixed by explicitly using __INT32_TYPE__ for targets with __SIZEOF_INT__ < 4.

gcc/testsuite/

2017-05-09  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>

	* gcc.dg/tree-ssa/cunroll-13.c: Use __INT32_TYPE__ for
	for targets with __SIZEOF_INT__ < 4.

From-SVN: r247782