function signbitf( x ) {
	return Boolean( addon( x ) );
}
Returns a boolean indicating if the sign bit is on (true) or off (false).

@private
@param {number} x - input value
@returns {boolean} - boolean indicating if sign bit is on or off

@example
var toFloat32 = require( '@stdlib/number/float64/base/to-float32' );

var bool = signbitf( toFloat32( 4.0 ) );
// returns false

@example
var toFloat32 = require( '@stdlib/number/float64/base/to-float32' );

var bool = signbitf( toFloat32( -9.14e-34 ) );
// returns true

@example
var bool = signbitf( 0.0 );
// returns false

@example
var bool = signbitf( -0.0 );
// returns true