Update to cap-std 0.19.0 and rsix 0.22.4. (#3331)

This pulls in the s390x fix needed by #3330.

Also a small `rsix` API update; `PollFdVec` has been removed in favor of
just using `Vec<PollFd>`.

crates/wasi-common/Cargo.toml

@@ -22,13 +22,13 @@ anyhow = "1.0"
 thiserror = "1.0"
 wiggle = { path = "../wiggle", default-features = false, version = "0.29.0" }
 tracing = "0.1.19"
-cap-std = "0.18.0"
-cap-rand = "0.18.0"
+cap-std = "0.19.0"
+cap-rand = "0.19.0"
 bitflags = "1.2"
 io-lifetimes = { version = "0.3.0", default-features = false }
 
 [target.'cfg(unix)'.dependencies]
-rsix = "0.20.4"
+rsix = "0.22.4"
 
 [target.'cfg(windows)'.dependencies]
 winapi = "0.3"