Sync with Rust post C-variadic PR
The rustc PR "Support defining C compatible variadic functions" adds
support for defining C-compatible variadic functions in Rust. and
adds the `TyKind` variant `CVarArgs`. Update `syn` to also parse
Rust defined C-compatible variadic functions.
diff --git a/tests/clone.sh b/tests/clone.sh
index eb0df7d..063fec6 100755
--- a/tests/clone.sh
+++ b/tests/clone.sh
@@ -1,6 +1,6 @@
#!/bin/bash
-REV=e2f221c75932de7a29845c8d6f1f73536ad00c41
+REV=1999a2288123173b2e487865c9a04386173025f7
set -euo pipefail
cd "$(dirname "${BASH_SOURCE[0]}")"