Please backport eb2ba2ea953b5e to 10.x ([CUDA] Warn about unsupported CUDA SDK version only if it's used)

[llvmbot]

Bugzilla Link	45270
Resolution	FIXED
Resolved on	Mar 23, 2020 08:23
Version	10.0
OS	Linux
Blocks	#43900
Attachments	0001-CUDA-Warn-about-unsupported-CUDA-SDK-version-only-if.patch (rebased)
Reporter	LLVM Bugzilla Contributor
CC	@Rombur,@zmodem,@zygoloid

Extended Description

We've gotten a bug report today indicating that the new clang version throws warning about unsupported CUDA versions unconditionally (even when not using CUDA). This means that if the user happens to have newer CUDA installed, a lot of CMake checks fail wrongly, and it can't even compile LLVM correctly.

I realize that it's really late for fixes but I think this is a serious blocker. I'm attaching a rebased version of the following commit:

commit eb2ba2e
Author: Artem Belevich tra@google.com
Date: 2020-03-11 22:53:03 +0100

[CUDA] Warn about unsupported CUDA SDK version only if it's used.

This fixes an issue with clang issuing a warning about unknown CUDA SDK if it's
detected during non-CUDA compilation.

Differential Revision: https://reviews.llvm.org/D76030

[zmodem]

I guess I had underestimated the importance of this :( Merged as d32170d