Log Message:
sysutils/xosview2: update to xosview2-2.3.3

Add c++17 to USE_LANGUAGES to support `std::optional'.

Changes since xosview-2.3.2:

 - reduce area cleared by labels by 1.

 - switch to std::optional

 - xsm now builds again.

 Changes since xosview-2.3.1
 - fix openbsd cpu meter for new systemctl stats.

 - move BSD battery meter related code into btrymeter.cc.

 - fix freebsd memory meter for new sysctl stats.

 -  remove dragonfly no longer has apmbios related battery
    stats.

 - misc cleanups.