Fix bogus test failure for avr

The test has a bunch of hardcoded integer literals that would fit only in a 
32 bits+ int, causing overflow warnings for a 16 bit int target like avr.

gcc/testsuite/ChangeLog

2016-09-27  Senthil Kumar Selvaraj  <senthil_kumar.selvaraj@atmel.com>

	* gcc.dg/tree-ssa/builtin-sprintf-warn-1.c: Require int32plus.

From-SVN: r240528