[CC Hans in case we can improve some things in the clang-cl driver]
-Xclang is horrible. Please add a FIXME assigned to you to remove this as soon as the necessary flags are supported by clang-cl.
Why do you need this? If there is no libstdc++ on Windows, you should instead detect this in the build system and introduce
Landed everything except for one questionable if() in r208682.
We had an offline discussion here and wonder why doesn't the driver itself pass this flag?
We also have to do if(NOT MSVC) for the recently-introduced --driver=g++ flag here anyways, so not clear if the extra variable is worth it.
(we can probably discuss that on the commit email)