python support appears broken in the ports trree

[Chris]

I've spent the past 2 days attempting a fresh build/install
of world/kernel && preferred ports/applications. The world/kernel
worked to perfection. But I can *not* get the ports to build,
and install. All *fatal* errors stem from python.
So after booting into a new world/kernel; I proceed to build/install
perl5-5.30, python27 && python37. I now feel I have the versions I
need/want. So I move to /usr/ports/x11/xorg and perform a
make config-recursive until the dialogs will no longer appear.
>From there (today) make(1) terminates at:
...
===>  Staging for xorg-7.7_3
===>   xorg-7.7_3 depends on file: /usr/local/libdata/pkgconfig/dri.pc - not found
===>   mesa-dri-18.3.2_9 depends on package: wayland-protocols>=1.8 - found
===>   mesa-dri-18.3.2_9 depends on file: /usr/local/libdata/pkgconfig/pthread-stubs.pc - found
===>   mesa-dri-18.3.2_9 depends on executable: bison - found
===>   mesa-dri-18.3.2_9 depends on executable: msgfmt - found
===>   mesa-dri-18.3.2_9 depends on executable: gmake - found
===>   mesa-dri-18.3.2_9 depends on package: pkgconf>=1.3.0_1 - found
===>   mesa-dri-18.3.2_9 depends on file: /usr/local/bin/python2.7 - found
===>   mesa-dri-18.3.2_9 depends on package: llvm80>=3.9.0_4 - not found
===>  llvm80-8.0.1_3 needs Python 3.6 at least, but 2.7 was specified.
*** Error code 1

...

I struggled all day yesterday with various ports barfing with similar
python messages. So today I blew everything off the disk, and started
from scratch. Which only repeats what happened yesterday. Is python
multiplicity no longer available? Or?

make.conf(5)
DEFAULT_VERSIONS+=tcl=8.7 tk=8.7

FreeBSD eleventhree 11.3-RELEASE-p5 FreeBSD 11.3-RELEASE-p5 #0 r355580: Tue Dec 10 13:22:30 PST 2019
root at eleventhree:/usr/obj/usr/src/sys/ELEVENTHREE  amd64

Path: /usr/src
Working Copy Root Path: /usr/src
URL: svn://svn.freebsd.org/base/releng/11.3
Relative URL: ^/releng/11.3
Repository Root: svn://svn.freebsd.org/base
Repository UUID: ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
Revision: 355580
Node Kind: directory
Schedule: normal
Last Changed Author: gordon
Last Changed Rev: 354654
Last Changed Date: 2019-11-12 10:13:51 -0800 (Tue, 12 Nov 2019)

Path: /usr/ports
Working Copy Root Path: /usr/ports
URL: svn://svn.freebsd.org/ports/head
Relative URL: ^/head
Repository Root: svn://svn.freebsd.org/ports
Repository UUID: 35697150-7ecd-e111-bb59-0022644237b5
Revision: 519768
Node Kind: directory
Schedule: normal
Last Changed Author: pizzamig
Last Changed Rev: 519768
Last Changed Date: 2019-12-10 09:39:01 -0800 (Tue, 10 Dec 2019)

Thank you for all your time, and consideration.

--Chris