[Bug target/121959] riscv: vector sign extend instead of zero extend

[pan2.li at intel dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=121959

--- Comment #3 from Li Pan <pan2.li at intel dot com> ---
Created attachment 62449
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=62449&action=edit
vwsll