clang-8: error: unknown argument: '-flto-partition=none' when building lxml

[Luke Benes]

> uses $$CFLAGS (i.e., whathever the CFLAGS env var is set to
in the shell run by `make`) 

It's not coming from shell CFLAGS. I have searched all shell and environment variables with:
$( set -o posix ; set ) | less
And nothing has a '-flto-partition=none'  

Any other ideas on where to find this or how to override it?

This is definitely distro specific, as Ubuntu still works fine. Also, it was a fairly recent change in Arch. Could it have happened when I upgraded gcc, or if not what might it be?

Thanks,

-Luke