emulators/virtualbox-ose{,-legacy}: sort out options

Sort out options: order (portlint), convert to OPTION_*.
Add entry in "Troubleshooting" about "VERR_NO_MEMORY".
Force devel/llvm15 for emulators/virtualbox-ose-legacy on recent 14 with
llvm16 in base.

PR: 200764 252227
Approved by: arrowd (mentor)
Differential Revision: https://reviews.freebsd.org/D40751