Use rsix to make system calls in Wasmtime. (#3355)

* Use rsix to make system calls in Wasmtime.

`rsix` is a system call wrapper crate that we use in `wasi-common`,
which can provide the following advantages in the rest of Wasmtime:

 - It eliminates some `unsafe` blocks in Wasmtime's code. There's
   still an `unsafe` block in the library, but this way, the `unsafe`
   is factored out and clearly scoped.

 - And, it makes error handling more consistent, factoring out code for
   checking return values and `io::Error::last_os_error()`, and code that
   does `errno::set_errno(0)`.

This doesn't cover *all* system calls; `rsix` doesn't implement
signal-handling APIs, and this doesn't cover calls made through `std` or
crates like `userfaultfd`, `rand`, and `region`.

crates/jit/Cargo.toml

@@ -25,15 +25,17 @@ gimli = { version = "0.25.0", default-features = false, features = ["std", "read
 object = { version = "0.26.0", default-features = false, features = ["std", "read_core", "elf"] }
 serde = { version = "1.0.94", features = ["derive"] }
 addr2line = { version = "0.16.0", default-features = false }
-libc = { version = "0.2.60", default-features = false, optional = true }
 ittapi-rs = { version = "0.1.5", optional = true  }
 bincode = "1.2.1"
 
 [target.'cfg(target_os = "windows")'.dependencies]
 winapi = { version = "0.3.8", features = ["winnt", "impl-default"] }
 
+[target.'cfg(target_os = "linux")'.dependencies]
+rsix = { version = "0.23.0", optional = true }
+
 [features]
-jitdump = ['libc']
+jitdump = ['rsix']
 vtune = ['ittapi-rs']
 
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