First steps towards vs2019 optional feedstock

[geoffreygarrett]

A large package of mine (10k lines of code) fails when compiling with vs2017 with internal compiler errors, however it passes with vs2019. Other platforms pass as well. Following a discussion with @beckermr, he chaired a talking point at the conda-forge/core team meeting concerning making vs2019 a supported feedstock. The minutes recorded are as follow.

• What do we need to do to get this done?
  • (@isuruf) Is this going to be global or just for a few feedstocks? If it's global, that's going to be a bit of a problem. you can link libs with 2017 and 2019 together, but you need 2019 to do the linking. This will require people building conda packages locally to update to vs2019. Uwe was cross-compiling but we only have vs2017.
  • Which feedstocks need to be updated? Just the vc one
  • new universal runtime which adds new DLLs
    • not on windows 10
    • can download it from windows update
    • make a new runtime package
    • @jjhelmus posted a note on the filename in gitter
      • try and use paul's PR for vc for 2019
      • do that PR for 2017 and try it on vc_dev channel
    • then do for 2019
    • keep track of where version numbers come from

[beckermr]

This is the 2019 PR: #19.

We should get that to work for 2017 first.