Change proc_exit to unwind the stack rather than exiting the host process. (#1646)

* Remove Cranelift's OutOfBounds trap, which is no longer used.

* Change proc_exit to unwind instead of exit the host process.

This implements the semantics in https://github.com/WebAssembly/WASI/pull/235.

Fixes #783.
Fixes #993.

* Fix exit-status tests on Windows.

* Revert the wiggle changes and re-introduce the wasi-common implementations.

* Move `wasi_proc_exit` into the wasmtime-wasi crate.

* Revert the spec_testsuite change.

* Remove the old proc_exit implementations.

* Make `TrapReason` an implementation detail.

* Allow exit status 2 on Windows too.

* Fix a documentation link.

* Really fix a documentation link.

tests/all/cli_tests.rs

@@ -182,3 +182,77 @@ fn timeout_in_invoke() -> Result<()> {
     );
     Ok(())
 }
+
+// Exit with a valid non-zero exit code, snapshot0 edition.
+#[test]
+fn exit2_wasi_snapshot0() -> Result<()> {
+    let wasm = build_wasm("tests/wasm/exit2_wasi_snapshot0.wat")?;
+    let output = run_wasmtime_for_output(&[wasm.path().to_str().unwrap(), "--disable-cache"])?;
+    assert_eq!(output.status.code().unwrap(), 2);
+    Ok(())
+}
+
+// Exit with a valid non-zero exit code, snapshot1 edition.
+#[test]
+fn exit2_wasi_snapshot1() -> Result<()> {
+    let wasm = build_wasm("tests/wasm/exit2_wasi_snapshot1.wat")?;
+    let output = run_wasmtime_for_output(&[wasm.path().to_str().unwrap(), "--disable-cache"])?;
+    assert_eq!(output.status.code().unwrap(), 2);
+    Ok(())
+}
+
+// Exit with a valid non-zero exit code, snapshot0 edition.
+#[test]
+fn exit125_wasi_snapshot0() -> Result<()> {
+    let wasm = build_wasm("tests/wasm/exit125_wasi_snapshot0.wat")?;
+    let output = run_wasmtime_for_output(&[wasm.path().to_str().unwrap(), "--disable-cache"])?;
+    if cfg!(windows) {
+        assert_eq!(output.status.code().unwrap(), 1);
+    } else {
+        assert_eq!(output.status.code().unwrap(), 125);
+    }
+    Ok(())
+}
+
+// Exit with a valid non-zero exit code, snapshot1 edition.
+#[test]
+fn exit125_wasi_snapshot1() -> Result<()> {
+    let wasm = build_wasm("tests/wasm/exit125_wasi_snapshot1.wat")?;
+    let output = run_wasmtime_for_output(&[wasm.path().to_str().unwrap(), "--disable-cache"])?;
+    if cfg!(windows) {
+        assert_eq!(output.status.code().unwrap(), 1);
+    } else {
+        assert_eq!(output.status.code().unwrap(), 125);
+    }
+    Ok(())
+}
+
+// Exit with an invalid non-zero exit code, snapshot0 edition.
+#[test]
+fn exit126_wasi_snapshot0() -> Result<()> {
+    let wasm = build_wasm("tests/wasm/exit126_wasi_snapshot0.wat")?;
+    let output = run_wasmtime_for_output(&[wasm.path().to_str().unwrap(), "--disable-cache"])?;
+    if cfg!(windows) {
+        assert_eq!(output.status.code().unwrap(), 3);
+    } else {
+        assert_eq!(output.status.code().unwrap(), 128 + libc::SIGABRT);
+    }
+    assert!(output.stdout.is_empty());
+    assert!(String::from_utf8_lossy(&output.stderr).contains("invalid exit status"));
+    Ok(())
+}
+
+// Exit with an invalid non-zero exit code, snapshot1 edition.
+#[test]
+fn exit126_wasi_snapshot1() -> Result<()> {
+    let wasm = build_wasm("tests/wasm/exit126_wasi_snapshot1.wat")?;
+    let output = run_wasmtime_for_output(&[wasm.path().to_str().unwrap(), "--disable-cache"])?;
+    if cfg!(windows) {
+        assert_eq!(output.status.code().unwrap(), 3);
+    } else {
+        assert_eq!(output.status.code().unwrap(), 128 + libc::SIGABRT);
+    }
+    assert!(output.stdout.is_empty());
+    assert!(String::from_utf8_lossy(&output.stderr).contains("invalid exit status"));
+    Ok(())
+}