rust: Vendor literal parsing from syn crate

`module!` macro currently have some ad-hoc literal
parsing. `syn` crate provides some proper parsing
for us to use.

Signed-off-by: Gary Guo <[email protected]>

Author: nbdd0121

rust/macros/lib.rs

@@ -2,6 +2,7 @@
 
 //! Crate for all kernel procedural macros.
 mod module;
+mod syn;
 
 use proc_macro::TokenStream;