--use-strict flag doesn't apply strict mode to script

* Node 12.*: * Windows 64bit, Debian 64bit: The `--use-strict` flag doesn't apply strict mode to script. reproduction: ``` echo a = 1 > test.js && node --use-strict test ``` expected behavior: `ReferenceError: a is not defined` is thrown. behavior: script executes without any issue. however it works as expected when node is started first and script is called from repl. <12 versions aren't affected. ``` node --use-strict Welcome to Node.js v12.12.0. Type ".help" for more information. > a = 1 Thrown: ReferenceError: a is not defined > ```