Move the filetest harness into its own crate.

This allows us to run the tests via a library call rather than just
as a command execution. And, it's a step toward a broader goal, which
is to keep the code in the top-level src directory minimal, with
important functionality exposed as crates.

cranelift/tests/cton-util-test.rs

@@ -1,34 +0,0 @@
-//! Run `cton-util test` on all available testcases.
-
-use std::process::{Command, Output};
-use std::env;
-use std::path::PathBuf;
-use std::io::{self, Write};
-
-/// Returns the target directory, where we can find build artifacts
-/// and such for the current configuration.
-fn get_target_dir() -> PathBuf {
-    let mut path = env::current_exe().unwrap();
-    path.pop(); // chop off exe name
-    path.pop(); // chop off deps name
-    path
-}
-
-#[test]
-fn cton_util_test() {
-    let mut cmd = Command::new(&get_target_dir().join("cton-util"));
-    cmd.arg("test");
-
-    // We have testcases in the following directories:
-    cmd.arg("filetests");
-    cmd.arg("docs");
-
-    let Output {
-        status,
-        stdout,
-        stderr,
-    } = cmd.output().unwrap();
-    io::stdout().write(&stdout).unwrap();
-    io::stderr().write(&stderr).unwrap();
-    assert!(status.success(), "failed with exit status {}", status);
-}

cranelift/tests/filetests.rs

@@ -0,0 +1,7 @@
+extern crate cton_filetests;
+
+#[test]
+fn filetests() {
+    // Run all the filetests in the following directories.
+    cton_filetests::run(false, vec!["filetests".into(), "docs".into()]).expect("test harness");
+}