RISC-V: Fix dead loop for user vsetvli intrinsic avl checking [PR109773]

RISC-V: Fix dead loop for user vsetvli intrinsic avl checking [PR109773]

This patch is fix dead loop in vsetvl intrinsic avl checking.

vsetvli->get_def () has vsetvli->get_def () has vsetvli.....
Then it will keep looping in the vsetvli avl checking which is a dead loop.

	PR target/109773

gcc/ChangeLog:

	* config/riscv/riscv-vsetvl.cc (avl_source_has_vsetvl_p): New function.
	(source_equal_p): Fix dead loop in vsetvl avl checking.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/vsetvl/pr109773-1.c: New test.
	* gcc.target/riscv/rvv/vsetvl/pr109773-2.c: New test.