If you already have your own functions or variables named max, min, or clear in-scope, they will shadow the new built-in functions and your code will continue to use your own version of the functions. No breakage to existing identifiers that match the new function names.
(This is the same behavior as the append built-in function today, for example. These things in Go are _not_ reserved keywords, they are simply global functions that can be overridden at other scopes.)