Log Message:
PC6001VX: update to 3.9.1.

Note this is the last version of PC6001VX 3.x that uses Qt5, and
PC6001VX 4.x has already been released and switched to using Qt6.
I'll update to 4.x soon after I commit a qt6-qtbase fix for NetBSD/i386.

Upstream changes:

3.9.1 2023/01/01
* Updated PC-6001mk2/6601 compatible basic ROMs to 0.4.1.