fix: staticcheck and deadcode findings repo-wide, modernize counting loops

debug/target_linux_amd64.go

@@ -98,10 +98,10 @@ func RunTarget(asmPath, funcName, argsFile, tmpDir string) error {
 	stackArgs := make([]byte, fl.Args)
 	copy(stackArgs, args)
 
-	_, callErr := verify.Call(fnAddr, stackArgs)
-	if callErr != nil {
+	if _, callErr := verify.Call(fnAddr, stackArgs); callErr != nil {
 		os.Exit(1)
 	}
-	os.Exit(0)
+	// Success returns to the caller, which exits with status 0; the JIT
+	// code has already run to its own trampoline by the time Call returns.
 	return nil
 }