Error using `bindSym` at compile time

[Hlaaftana]

This is specific to `bindSym`. You need the experimental 
[dynamicBindSym](https://nim-lang.github.io/Nim/manual_experimental.html#dynamic-arguments-for-bindsym).
 I have a [PR open](https://github.com/nim-lang/Nim/pull/20125) which moves 
this to its own proc but it shouldn't be incompatible with normal uses of 
bindSym.