There is no corresponding syntax, but you can use explicit lookup:

print constant("classname::$myConst");

I believe it also works with self::.

There are two ways to do this: using a constant function or using reflection.

Constant function

Constant functions apply to constants declared via define as well as class constants:

class A
{
    const MY_CONST = 'myval';

    static function test()
    {
        $c = 'MY_CONST';
        return constant('self::'. $c);
    }
}

echo A::test(); // output: myval

Reflection class

The second, more laborious method is through reflection:

$ref = new ReflectionClass('A');
$constName = 'MY_CONST';
echo $ref->getConstant($constName); // output: myval