[COMMITTED] Remove TDF_THREADING flag in favor of param.

[Aldy Hernandez]

On Tue, Nov 9, 2021 at 3:10 PM Martin Liška <mliska@suse.cz> wrote:
>
> > +-param=threader-debug=
>
> Please document the param in gcc/doc/invoke.texi.

I purposely didn't document it.  This is an internal debugging
construct.  What's our policy on this?

I'm happy to do this; I just didn't want the CI bots trying weird
combinations and reporting PRs on the size of debugging dumps, etc.
;-)

Aldy