Previously casting a bool to an int would result in the following Zig code:

    @intCast(c_int, @bitCast(i1, @intCast(u1, @boolToInt(b))));

This is incorrect if `b` is true, since bitcasting a `u1` with the value 1
to an `i1` will result in the value -1. Instead, generate the following code:

    @as(c_int, @boolToInt(b));

Since @boolToInt returns a `u1`, this is only disallowed if the destination
type is one-bit and signed, which can only happen if it's a bitfield
(currently not supported by translate-c)