In this case you can just change the code as it is a warning from php telling you to use continue 2; As a matter of fact php already knows it should be continue 2; instead of continue; to jump out of the switch back to the for each element. WP core team will just make the same adjustment as php is suggesting in the next update.
Or just stick with the warning and or disable these php messages in order to avoid the headers already send problem which is worse then editing the core files.
There is nothing wrong with making these small adjustments as long as you know how to write code
just open the files in a ascii editor like notepad++ by ftp goto the corresponding lines as mentioned in the error and change
continue;
into continue 2;
It is really as easy as that.
https://stackoverflow.com/questions/26431066/continue-2-and-break-in-switch-statement