rust: syn: add SPDX License Identifiers

Originally, when the Rust upstream `alloc` standard library crate was
vendored in commit 057b8d2 ("rust: adapt `alloc` crate to the
kernel"), the SPDX License Identifiers were added to every file so that
the license on those was clear.

Thus do the same for the `syn` crate.

This makes `scripts/spdxcheck.py` pass.

Reviewed-by: Gary Guo <gary@garyguo.net>
Tested-by: Gary Guo <gary@garyguo.net>
Tested-by: Jesung Yang <y.j3ms.n@gmail.com>
Link: https://patch.msgid.link/20251124151837.2184382-17-ojeda@kernel.org
Signed-off-by: Miguel Ojeda <ojeda@kernel.org>

Author: ojeda

rust/syn/attr.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 #[cfg(feature = "parsing")]
 use crate::error::Error;
 #[cfg(feature = "parsing")]

rust/syn/bigint.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use std::ops::{AddAssign, MulAssign};
 
 // For implementing base10_digits() accessor on LitInt.

rust/syn/buffer.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! A stably addressed token buffer supporting efficient traversal based on a
 //! cheaply copyable cursor.
 

rust/syn/classify.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 #[cfg(feature = "full")]
 use crate::expr::Expr;
 #[cfg(any(feature = "printing", feature = "full"))]

rust/syn/custom_keyword.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 /// Define a type that supports parsing and printing a given identifier as if it
 /// were a keyword.
 ///

rust/syn/custom_punctuation.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 /// Define a type that supports parsing and printing a multi-character symbol
 /// as if it were a punctuation token.
 ///

rust/syn/data.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use crate::attr::Attribute;
 use crate::expr::{Expr, Index, Member};
 use crate::ident::Ident;

rust/syn/derive.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use crate::attr::Attribute;
 use crate::data::{Fields, FieldsNamed, Variant};
 use crate::generics::Generics;

rust/syn/discouraged.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 //! Extensions to the parsing API with niche applicability.
 
 use crate::buffer::Cursor;

rust/syn/drops.rs

@@ -1,3 +1,5 @@
+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
 use std::iter;
 use std::mem::ManuallyDrop;
 use std::ops::{Deref, DerefMut};