testsuite: Require int32plus target for gcc.dg/pr117816.c

Memmove destination overflows if size of int is less than 3, resulting in
spurious test failures.  Fix by adding a requirement for effective
target int32plus.

gcc/testsuite/ChangeLog:

	* gcc.dg/pr117816.c: Require effective target int32plus.

Signed-off-by: Dimitar Dimitrov <dimitar@dinux.eu>