* Add sccache to the Windows job
Also fix debug symbols on googletest,
so that it doesn't try to create a separate pdb.
* Fix uploading the submodule cache
sccache needs its cache to be uploaded as normal files,
not with a tar, otherwise the cache when extracted
will contain extraneous files and folders (PaxHeader).
The Files mode though by default ignores the .git folder,
so we have to use the .artifactignore file to unignore it,
and we have to copy in the cached path for the cache task to see it.
