Reorganize wasi-misc-tests. (#575)

* Reorganize wasi-misc-tests.

Move wasi-misc-tests out of wasi-common, to break a dependency cycle;
previously, wasmtime-* depended on wasi-common, but wasi-common
dev-dependended on wasmtime-*.

Now, wasi-common no longer dev-depends on wasmtime-*; instead, the
tests are in their own crate which depends on wasi-common and on
wasmtime-*.

Also, rename wasi-misc-tests to wasi-tests for simplicity.

This also removes the "wasm_tests" feature; it's replaced by the
"test-programs" feature.

* Update the CI script to use the new feature name.

* Update the CI script to use the new feature name in one more place.

* Change a `write!` to a `writeln!`.

crates/test-programs/wasi-tests/src/bin/readlink_no_buffer.rs

@@ -0,0 +1,51 @@
+use std::{env, process};
+use wasi::wasi_unstable;
+use wasi_tests::open_scratch_directory;
+use wasi_tests::utils::cleanup_file;
+use wasi_tests::wasi_wrappers::{wasi_path_readlink, wasi_path_symlink};
+
+unsafe fn test_readlink_no_buffer(dir_fd: wasi_unstable::Fd) {
+    // First create a dangling symlink.
+    assert!(
+        wasi_path_symlink("target", dir_fd, "symlink").is_ok(),
+        "creating a symlink"
+    );
+
+    // Readlink it into a non-existent buffer.
+    let mut bufused: usize = 1;
+    let status = wasi_path_readlink(dir_fd, "symlink", &mut [], &mut bufused);
+    assert_eq!(
+        status,
+        wasi_unstable::raw::__WASI_ESUCCESS,
+        "readlink with a 0-sized buffer should succeed"
+    );
+    assert_eq!(
+        bufused, 0,
+        "readlink with a 0-sized buffer should return 'bufused' 0"
+    );
+
+    // Clean up.
+    cleanup_file(dir_fd, "symlink");
+}
+fn main() {
+    let mut args = env::args();
+    let prog = args.next().unwrap();
+    let arg = if let Some(arg) = args.next() {
+        arg
+    } else {
+        eprintln!("usage: {} <scratch directory>", prog);
+        process::exit(1);
+    };
+
+    // Open scratch directory
+    let dir_fd = match open_scratch_directory(&arg) {
+        Ok(dir_fd) => dir_fd,
+        Err(err) => {
+            eprintln!("{}", err);
+            process::exit(1)
+        }
+    };
+
+    // Run the tests.
+    unsafe { test_readlink_no_buffer(dir_fd) }
+}