Thanks, Nico. I tried Fedora, and had the same problem, so I returned to Ubuntu and in summary:

removed old pciutils
installed pci.ids
per: https://github.com/RadeonOpenCompute/ROCT-Thunk-Interface/issues/7
installed libpci-dev
Got past: pci/pci.h: No such file or directory

Then failed:
"In file included from raiden_debug_spi.c:343:
usb_device.h:28:10: fatal error: libusb.h: No such file or directory
   28 | #include <libusb.h>
      |          ^~~~~~~~~~
compilation terminated.
make: *** [Makefile:1271: raiden_debug_spi.o] Error 1"

root@clay-MS-7C37:~# apt install libusb-dev

But same error: libusb.h missing :(

per: https://github.com/UltimateHackingKeyboard/agent/issues/407
"Thinking out loud here if I post this...
libusb.h is missing...
libusb-dev version is 2:0.1.12-30
There also exists the package libusb-1.0-0-dev
OK, install libusb-1.0-0-dev"

IT COMPILED !!!
root@clay-MS-7C37:~/flashrom# flashrom --version
flashrom v1.2-132-gdd81c9a on Linux 5.8.0-25-generic (x86_64)
flashrom is free software, get the source code at https://flashrom.org
root@clay-MS-7C37:~/flashrom#

Now I have a working self-compiled install of flashrom to play with. It does not seem to find my spi flash chip yet, but I'm working on it. Just being able to build the latest git version is a big step forward.

Thanks all,

clay