Add vect_recog_cond_expr_convert_pattern.

The pattern converts (cond (cmp a b) (convert c) (convert d))
to (convert (cond (cmp a b) c d)) when
1) types_match (c, d)
2) single_use for (convert c) and (convert d)
3) TYPE_PRECISION (TREE_TYPE (c)) == TYPE_PRECISION (TREE_TYPE (a))
4) INTEGERAL_TYPE_P (TREE_TYPE (c))

The pattern can save packing of mask and data(partial for data, 2 vs
1).

gcc/ChangeLog:

	PR target/103771
	* match.pd (cond_expr_convert_p): New match.
	* tree-vect-patterns.cc (gimple_cond_expr_convert_p): Declare.
	(vect_recog_cond_expr_convert_pattern): New.

gcc/testsuite/ChangeLog:

	* gcc.target/i386/pr103771-2.c: New test.
	* gcc.target/i386/pr103771-3.c: New test.