chore: add vendor dependencies for kauma build

vendor/syn/tests/zzz_stable.rs

@@ -0,0 +1,33 @@
+#![cfg(syn_disable_nightly_tests)]
+
+use std::io::{self, Write};
+use termcolor::{Color, ColorChoice, ColorSpec, StandardStream, WriteColor};
+
+const MSG: &str = "\
+‖
+‖   WARNING:
+‖   This is not a nightly compiler so not all tests were able to
+‖   run. Syn includes tests that compare Syn's parser against the
+‖   compiler's parser, which requires access to unstable librustc
+‖   data structures and a nightly compiler.
+‖
+";
+
+#[test]
+fn notice() -> io::Result<()> {
+    let header = "WARNING";
+    let index_of_header = MSG.find(header).unwrap();
+    let before = &MSG[..index_of_header];
+    let after = &MSG[index_of_header + header.len()..];
+
+    let mut stderr = StandardStream::stderr(ColorChoice::Auto);
+    stderr.set_color(ColorSpec::new().set_fg(Some(Color::Yellow)))?;
+    write!(&mut stderr, "{}", before)?;
+    stderr.set_color(ColorSpec::new().set_bold(true).set_fg(Some(Color::Yellow)))?;
+    write!(&mut stderr, "{}", header)?;
+    stderr.set_color(ColorSpec::new().set_fg(Some(Color::Yellow)))?;
+    write!(&mut stderr, "{}", after)?;
+    stderr.reset()?;
+
+    Ok(())
+}