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.

.github/workflows/main.yml

@@ -77,7 +77,7 @@ jobs:
         submodules: true
     - uses: ./.github/actions/install-rust
       with:
-        toolchain: nightly-2022-09-07
+        toolchain: nightly-2022-12-15
 
     # Build C API documentation
     - run: curl -L https://sourceforge.net/projects/doxygen/files/rel-1.9.3/doxygen-1.9.3.linux.bin.tar.gz/download | tar xzf -
@@ -197,7 +197,7 @@ jobs:
     # flags to rustc.
     - uses: ./.github/actions/install-rust
       with:
-        toolchain: nightly-2022-09-07
+        toolchain: nightly-2022-12-15
     - run: cargo install cargo-fuzz --vers "^0.11"
     # Install the OCaml packages necessary for fuzz targets that use the
     # `wasm-spec-interpreter`.