Step2: fixes #13781, fixes #13805

[cooldome]

Spawn for gc arc fixes

[Araq]

Suspicious logic. Why not at the end of the of nkCallkinds handling code like

if n[0].kind == nkSym and n[0].sym.magic == mSpawn:
  c.inSpawn.dec

?

[cooldome]

The idea is that spawn can be written in the following way:

spawn myproc(call1(), (let x = call2(); call3(x, 0))

I want c.inSpawn to be greater than zero only for myproc call but not for call2 and call3 in example above.

[cooldome]

I can't replicate CI test failures. I have tried 3 machines, 2 platforms and 3 compilers. All tests pass.
Don't know how to progress further

[Araq]

Well BSD says:

Category: arc
Name: tests/arc/tthread.nim C
Action: run
Result: reExitcodesDiffer
-------- Expected -------
exitcode: 0
--------- Given --------
exitcode: 1

Output:

---

[cooldome]

Ready for review