I have a test machine running 10.13.2 on a MacBook Pro Retina 2017 running an Intel Core i7. The below PoC C code works when compiled with the following command:
Save the below PoC code as "spectre.c"
The original code came from the spectre paper but required a tiny patch from a gist page to work on macOS (google it and you can find it)
If you run it, this is what you should expect: