Auto merge of #3452 - devnexen:solarish_self_fd, r=JohnTitor

expose solarish's SFV_FD_SELF for sendfilev purpose

Author: bors

src/unix/solarish/mod.rs

@@ -2588,6 +2588,9 @@ const _CMSG_DATA_ALIGNMENT: usize = ::mem::size_of::<::c_int>();
 
 const NEWDEV: ::c_int = 1;
 
+// sys/sendfile.h
+pub const SFV_FD_SELF: ::c_int = -2;
+
 const_fn! {
     {const} fn _CMSG_HDR_ALIGN(p: usize) -> usize {
         (p + _CMSG_HDR_ALIGNMENT - 1) & !(_CMSG_HDR_ALIGNMENT - 1)