It was added in 2014 in 732e0aa9fb84f1 with one use in Scalarizer.cpp.
That one use was then removed when porting to the new pass manager in
2018 in b6f76002d9158628e78.
While the RFC and the desire to get off of static initializers for
cl::opt all still stand, this code is now dead, and I think we should
delete this code until someone is ready to do the migration.
This change depends on a large mechanical cleanup of including
CommandLine.h, StringMap.h, and raw_ostream.h which I'll push shortly.