Source tree has many empty directories?

[Ian Lepore]

On Tue, 2019-09-10 at 11:01 -0600, Warner Losh wrote:
> However, please do *NOT* remove the sys/*/compile directories.
> 
> Warner

Uhhh... that's interesting.  I just nuked one of those on my system
yesterday, because it had been hanging around since 2013 and I had no
idea what was -- I just assumed the build machinery created it because
I had accidentally done a make in a wrong directory once.

So what are those directories about?  I'm not used to seeing mystery
directories appear inside a source tree.

-- Ian