libc-test: remove useless clone in build.rs

Author: chenx97

libc-test/build.rs

@@ -642,7 +642,7 @@ fn test_windows(target: &str) {
 
             // Windows uppercase structs don't have `struct` in front:
             t if is_struct => {
-                if ty.clone().chars().next().unwrap().is_uppercase() {
+                if ty.chars().next().unwrap().is_uppercase() {
                     t.to_string()
                 } else if t == "stat" {
                     "struct __stat64".to_string()