Use the sym operator for inline assembly (#5459)

* Use the `sym` operator for inline assembly

Avoids extra `#[no_mangle]` functions and undue symbols being exposed
from Wasmtime. This is a newly stabilized feature in Rust 1.66.0. I've
also added a `rust-version` entry to the `wasmtime` crate to try to head
off possible reports in the future about odd error messages or usage of
unstable features if the rustc version is too old.

* Fix a s390x warning

* Add `rust-version` annotation to Wasmtime crate

As the other main entrypoint for embedders.

Cargo.toml

@@ -11,6 +11,7 @@ repository = "https://github.com/bytecodealliance/wasmtime"
 readme = "README.md"
 edition.workspace = true
 default-run = "wasmtime"
+rust-version.workspace = true
 
 [lib]
 doctest = false
@@ -105,6 +106,7 @@ exclude = [
 version = "5.0.0"
 authors = ["The Wasmtime Project Developers"]
 edition = "2021"
+rust-version = "1.66.0"
 
 [workspace.dependencies]
 wasmtime = { path = "crates/wasmtime", version = "5.0.0", default-features = false }