bug#30364: 26.0.91; thread crash on macos

[Eli Zaretskii]

> From: Aaron Jensen <aaronjensen@gmail.com>
> Date: Sun, 18 Feb 2018 10:39:58 -0800
> Cc: Noam Postavsky <npostavs@gmail.com>, 30364@debbugs.gnu.org, 
>       Noam Postavsky <npostavs@users.sourceforge.net>, Alan Third 
> <alan@idiocy.org>
> 
> This seems relevant:
> https://developer.apple.com/library/content/qa/qa1419/_index.html

If threads get only 512KB of stack, it's a small wonder that they
crash in GC.  IME, you need at least 3MB to endure a full GC in Emacs.