emulators/wine-proton: Default to LLVM 15 (instead of 10 or 11)
Port dc3c11a883551eab418c265403c383b27bad8000 from emulators/wine:
If the user has set the default version of LLVM to 10 or 11, use LLVM 15 instead (rather than LLVM 12 as before). LLVM 15 is the current default in ports, so one less version to install in case. Plus it's what everyone else uses.
Approved by: maintainer (iwtcex@gmail.com)