Enable variant P0608R3 in C++17, update LLVM, overhaul variant/any/optional tests - #4713

Enable variant P0608R3 in C++17, update LLVM, overhaul variant/any/optional tests#4713

Stephan T. Lavavej (StephanTLavavej) merged 30 commits into

microsoft:mainmicrosoft/STL:mainfrom

StephanTLavavej:variant-overhaulStephanTLavavej/STL:variant-overhaulCopy head branch name to clipboard