Skip cufile and nvtx3 when cuda isn't found

[madsbk]

Closes #444

[Jacobfaib]

IMO, this is still a bit too verbose. As a user, I don't quite know what to do with this information. So I don't have cuFile, do I want it? If so, how do I get it? And what happens if I don't have it?

I'm not saying you need to provide explicit download and install instructions for it etc. but if you are going to raise a big scary warning about it, it would be nice to have some kind of explanation :)¹.

Note that CUDAToolKit will automatically come shipped with cuFile.

My suggestion would be either:

• Consider making this a hard error instead (i.e. REQUIRED).
• Or giving the user some way to silence the warning (KvikIO_SILENCE_MISSING_CUFILE or something like that).

Footnotes

1. Also consider the case where I know I definitely don't want cuFile (for whatever reason), there is no way to silence this warning. Now suppose I want to run my cmake files using -Werror (to catch cmake warnings), I have no way of doing that with this warning. ↩

[madsbk]

I see you point but let's add explicit options in another PR: #459.
For now, I have added:

message(
  WARNING "Cannot find cuFile - KvikIO will still work but won't use GPUDirect Storage (GDS)"
)

[madsbk]

/merge