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.)