RISC-V: Support vnclip idiom testcase [PR120378]

RISC-V: Support vnclip idiom testcase [PR120378]

This patch contains testcases for PR120378 after the change made to
support the vnclipu variant of the SAT_TRUNC pattern.

	PR target/120378

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/rvv/autovec/pr120378-1.c: New test.
	* gcc.target/riscv/rvv/autovec/pr120378-2.c: New test.
	* gcc.target/riscv/rvv/autovec/pr120378-3.c: New test.
	* gcc.target/riscv/rvv/autovec/pr120378-4.c: New test.

Signed-off-by: Edwin Lu <ewlu@rivosinc.com>