can't use `static seq[string] = ...` param

[timotheecour]

how can one use a static param of type seq? (note: I don't want to use an array as that would tie default value to be of same length as the param, which is useless for example when default value is @[])

following code fails:

Error: type mismatch: got <static[array[0..-1, empty]]([])> but expected 'static[seq[string]]'
  macro foo(a: static seq[string] = @[]): untyped = discard

macro foo(a: static seq[string] = @[]): untyped = discard
proc main()=
  foo()
main()

this affects https://github.com/c-blake/cligen/issues/66#issuecomment-444310617

[timotheecour]

• possible duplicate of https://github.com/nim-lang/Nim/issues/8524 but not sure (at least title of #8524 would need to be more general)
• likewise, possible duplicate of #6177 (and same comment)