In `Call::compile()` in case we have CSS var() function calls and the keyword value of the function call prefixed by `--`
and color property name prefixed by `@` are same, then avoid generation of duplicate CSS definitions.
The CSS/LESS callable argument values may not always be an array, but also an object or whateever,
in this case we don't need to precompile the values as they could never be a variable.
