CONFIGURE: Make 32bit pointer check a bit safer.

This adapts the check to be similar to the find_type_with_size check, i.e. it
assigns a value to test_array and also returns 0. Should not be required, at
least builtbot went fine, but better be safe and sorry.

configure

@@ -1712,6 +1712,8 @@ pointer_is_32bit() {
 	cat > tmp_pointer_is_32bit.cpp << EOF
 int main() {
 	static int test_array[1 - 2 * !(sizeof(void *) == 4)];
+	test_array[0] = 0;
+	return 0;
 }
 EOF
 	$CXX $CXXFLAGS -c -o $TMPO.o tmp_pointer_is_32bit.cpp 2>/dev/null