Breakage in libvdpau package

[Arthur Barlow]

I'm running 12.1-RELEASE-p1 on amd64.  I did a portsnap today and then
tried to update three ports from source including libvdpau.  The first
package ffmpeg-4.2.1 built fine.  But, then in trying to build
libvdpau-1.3, I got the error message:

Traceback (most recent call last):
  File "/usr/local/bin/meson", line 6, in <module>
    from pkg_resources import load_entry_point
ModuleNotFoundError: No module named 'pkg_resources'
===>  Script "configure" failed unexpectedly.

I had recently followed the advise in UPDATE for ports and switched all my
"py36-*" programs to "py37-*" programs, so I don't know if that's a factor.

Thanks for the help.