Installing / Compiling Stable 2.8 on Debian 10 (Buster) issue with .configure

Hi all, I apologize in advance if this is a bone-headed question, but I'm trying to compile LinuxCNC and have followed instructions from here: linuxcnc.org/docs/master/html/code/building-linuxcnc.html .  I also checked these against the documentation within the git repository at /master/docs/INSTALL.adoc

The answer is I'm probably downloading the wrong repository or looking at the wrong instructions.

Either way, here's my problem. 

These two steps work:

But then it goes off the rails: both of those docs I mention above suggest the next step is to issue the command:

Gives me the following error message:
And if I try to move on to the next step in the instructions:

It just informs me that: 
It looks like there is a script called config.sub, and another called config.guess but I was cautious about jumping to try and use that script instead, given that it also seem autogen is looking for targets inside configure and issuing a touch command depending on what it finds, and at that point I'm getting lost in the fog of what needs to unfold.

There is also a note inside the file configure.ac whose comments say I'm supposed to feed this to autogen... ie, am I supposed to say ./autogen configure.ac  ??

Any help would be great, and thank you all for a great environment.

PS, on my machine, I have a "$" prompt... ie,
user@machineCNC:~/linuxcnc-dev/src$

Am I supposed to be in an interpreter environment or something? Because the documentation is using a ">" prompt. That would be the kind of inexperienced mistake I would make, but I didn't see direction in the documentation to start such an environment. 

PPS: I'm on a Buster system that I upgraded from Stretch. It is an ARM64 Single Board Computer, and it is running a preempt-rt kernel.

PPPS: I did not install git-all, only git.

Thanks again.

Thanks again for everyone's quick response.

I guess, doink, I was expecting the fail after the first line, not the first line. Doh. I'd seen that set of documentation, but didn't think it was relevant yet.

Sheepishly slinking away to run dpkg-checkbuilddeps...