testsuite: Unbreak pr110557.cc where long is 32-bit

On ports with 32-bit long, the test produced excess errors:

    gcc/testsuite/g++.dg/vect/pr110557.cc:12:8: warning: width of
    'Item::y' exceeds its type

Reported-by: Prathamesh Kulkarni <prathamesh.kulkarni@linaro.org>

gcc/testsuite/ChangeLog:

	* g++.dg/vect/pr110557.cc: Use long long instead of long for
	64-bit type.
	(test): Remove an unnecessary cast.