vect: Tighten an assertion for lane-reducing in transform

vect: Tighten an assertion for lane-reducing in transform

According to logic of code nearby the assertion, all lane-reducing operations
should not appear, not just DOT_PROD_EXPR. Since "use_mask_by_cond_expr_p"
treats SAD_EXPR same as DOT_PROD_EXPR, and WIDEN_SUM_EXPR should not be allowed
by the following assertion "gcc_assert (commutative_binary_op_p (...))", so
tighten the assertion.

2024-06-16 Feng Xue <fxue@os.amperecomputing.com>

gcc/
	* tree-vect-loop.cc (vect_transform_reduction): Change assertion to
	cover all lane-reducing ops.