Fix Swift 5.8 compatibility (#158)

We still use 5.8 as a bootstrap compiler on CI, so we need to make sure
that the code is compatible with it.

Author: kateinoigakukun

Sources/SwiftSDKGenerator/Generator/SwiftSDKGenerator+Copy.swift

@@ -121,8 +121,8 @@ extension SwiftSDKGenerator {
 extension Triple {
   var interpreterPath: String {
     switch self.archName {
-      case "x86_64": "/lib64/ld-linux-x86-64.so.2"
-      case "aarch64": "/lib/ld-linux-aarch64.so.1"
+      case "x86_64": return "/lib64/ld-linux-x86-64.so.2"
+      case "aarch64": return "/lib/ld-linux-aarch64.so.1"
       default: fatalError("unsupported architecture \(self.archName)")
     }
   }