[RISC-V] Adjust rvv tests after recent jump threading change

[RISC-V] Adjust rvv tests after recent jump threading change

Richi's jump threading patch is resulting in new jump threading opportunities
triggering in various vsetvl related tests.  When those new threading
opportunities are realized on vector code we usually end up with a different
number of vsetvls due to the inherent block copying.

At first I was adjusting cases to work with the new jump threads, then realized
we could easily end up back here if we change the threading heuristics and
such.  So I just made these tests disable jump threading.  I didn't do it
pervasively, just for those that have been affected.

gcc/testsuite

	* gcc.target/riscv/rvv/vsetvl/avl_prop-2.c: Disable jump threading
	and adjust number of expected vsetvls as needed.
	* gcc.target/riscv/rvv/vsetvl/avl_single-56.c: Likewise.
	* gcc.target/riscv/rvv/vsetvl/avl_single-67.c: Likewise.
	* gcc.target/riscv/rvv/vsetvl/avl_single-68.c: Likewise.
	* gcc.target/riscv/rvv/vsetvl/avl_single-71.c: Likewise.