vect: Fix an ICE in vect_recog_mask_conversion_pattern

vect: Fix an ICE in vect_recog_mask_conversion_pattern

When processing the cond expression, vect_recog_mask_conversion_pattern
doesn't consider the situation that two operands of rhs1 are different
vectypes, leading to a vect ICE. This patch adds the identification and
handling of the situation to fix the problem.

gcc/ChangeLog:

	PR target/96757
	* tree-vect-patterns.c (vect_recog_mask_conversion_pattern): Add
	the identification and handling of the dropped situation in the
	cond expression processing phase.

gcc/testsuite/ChangeLog:

	PR target/96757
	* gcc.target/aarch64/pr96757.c: New test.