The C equivalent of the Go expression x &^ y is just x & ~y. That is literally “x AND (bitwise NOT of y)”.
In the arithmetic operators section of the spec describes &^ as a “bit clear” operation, which gives an idea of what you’d want to use it for. As two separate operations, ~y will convert each one bit to a zero, which will then clear the corresponding bit in x. Each zero bit will be converted to a one, which will preserve the corresponding bit in x.
So if you think of x | y as a way to turn on certain bits of x based on a mask constant y, then x &^ y is doing the opposite and turns those same bits off.