fix illegal capture if forZip called within a proc

[Vindaar]

On my current Nim devel branch (from yesterday 26/04/18)

Nim Compiler Version 0.18.1 [Linux: amd64]
Copyright (c) 2006-2018 by Andreas Rumpf

git hash: 397e1731393be598991df302006ec3634baa3583
active boot switches: -d:release

Link to commit: nim-lang/Nim@397e173

loopfusion raises an illegal capture error, if forZip is used within a proc. To take a simple example from the loopfusion tests:

import loopfusion
    
proc main() =
  let a = @[1, 2, 3]
  let b = @[11, 12, 13]
  let c = @[10, 10, 10]

  forZip x in a, y in b, z in c:
    echo (x + y) * z

when isMainModule:
  main()

raises

~/.nimble/pkgs/loopfusion-0.0.1/loopfusion.nim(122, 15) Error: illegal capture 'a' because 'loopfusion_zipImpl_3_' has the calling convention: <inline>

while the same code, if placed directly below when isMainModule, compiles just fine.

The error refers to the usage of quote do here:

zipBody.add quote do:
   let `size0` = `container0`.len

By exchanging the usage of quote do with manual AST generation, the problem disappears.

[mratsim]

Awesome, thanks