Add build script to rustc_attr because of cfg(version)

Author: mibac138

src/librustc_attr/Cargo.toml

@@ -3,6 +3,7 @@ authors = ["The Rust Project Developers"]
 name = "rustc_attr"
 version = "0.0.0"
 edition = "2018"
+build = "build.rs"
 
 [lib]
 name = "rustc_attr"

src/librustc_attr/build.rs

@@ -0,0 +1,4 @@
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+    println!("cargo:rerun-if-env-changed=CFG_VERSION");
+}