perldoc perlop's Symbolic Unary Operators section explains this unary minus:

Unary "-" performs arithmetic negation if the operand is numeric, including any string that looks like a number. If the operand is an identifier, a string consisting of a minus sign concatenated with the identifier is returned.

In effect, it makes a bareword an unambiguous string constant. There's nothing special about this syntax when used in import lists (except that you'd have to write something like use English '-no_match_vars'; as an equivalent.)