Don't check can_vec_perm_const_p for nonlinear iv_init when it's constant.

Don't check can_vec_perm_const_p for nonlinear iv_init when it's constant.

When init_expr is INTEGER_CST or REAL_CST, can_vec_perm_const_p is not
necessary since there's no real vec_perm needed, but
vec_gen_perm_mask_checked will gcc_assert (can_vec_perm_const_p). So
it's better to use vec_gen_perm_mask_any in
vect_create_nonlinear_iv_init.

gcc/ChangeLog:

	PR tree-optimization/106963
	* tree-vect-loop.cc (vect_create_nonlinear_iv_init): Use
	vec_gen_perm_mask_any instead of vec_gen_perm_mask_check.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr106963.c: New test.