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A friend to all is a friend to none.
Literal
Ten-thousand-people [of-の] friend [topic-は] anyone [of-の] friend [even-でも] is-not.
A Japanese rendering of the Western proverb attributed to Aristotle: 'A friend to all is a friend to none.' The structure mirrors the English because of the negative-concord construction 誰の友でもない 'not anyone's friend,' where でも following an interrogative creates universal negation. 万人 'ten thousand people' is a formal, slightly literary expression for 'all people' or 'everyone,' common in aphorisms and formal speech.