transpile: save separate .{platform}.rs files for platform-specific snapshots

Author: kkysen

c2rust-transpile/tests/snapshots.rs

@@ -61,10 +61,18 @@ fn transpile(platform: Option<&str>, c_path: &Path) {
     let c_path = c_path.strip_prefix(&cwd).unwrap();
     let rs_path = c_path.with_extension("rs");
     let rs = fs::read_to_string(&rs_path).unwrap();
+    let rs_path = match platform {
+        None => rs_path,
+        Some(platform) => {
+            let platform_rs_path = rs_path.with_extension(&format!("{platform}.rs"));
+            fs::rename(&rs_path, &platform_rs_path).unwrap();
+            platform_rs_path
+        }
+    };
     let debug_expr = format!("cat {}", rs_path.display());
 
     let name = platform
-        .map(|platform| ["transpile", platform].join("-"))
+        .map(|platform| format!("transpile-{platform}"))
         .unwrap_or("transpile".into());
 
     insta::assert_snapshot!(name, &rs, &debug_expr);