build: Bump Cuda minimum to 9.0 (#1737)

Based on Brecht's tests, we realize that OSL doesn't work at all with
Cuda 8.0 (which didn't support the C++14 that we use), so we're
raising the minimum to 9.0. And there are some flaky tests with 9 and
10, so we're making the recommended minimum be 11.0.

It's not our policy to change the minimum versions of dependencies on
release branches, but I think we should backport this to the release
branch. I believe what this change is doing is not removing actual
support for old versions, but rather, correctly documenting what has
been working (or not) for quite some time.

---------

Signed-off-by: Larry Gritz <[email protected]>
Co-authored-by: Brecht Van Lommel <[email protected]>

INSTALL.md

@@ -45,7 +45,7 @@ NEW or CHANGED dependencies since the last major release are **bold**.
   on the OSL side to be compatible.
 
 * (optional) For GPU rendering on NVIDIA GPUs:
-    * [Cuda](https://developer.nvidia.com/cuda-downloads) 8.0 or higher.
+    * [Cuda](https://developer.nvidia.com/cuda-downloads) 9.0 or higher.
     * [OptiX](https://developer.nvidia.com/rtx/ray-tracing/optix) 5.1 or higher
       (though 7.0+ is highly recommended).
 

src/cmake/externalpackages.cmake

@@ -192,8 +192,11 @@ if (USE_CUDA OR USE_OPTIX)
         endif ()
 
         checked_find_package (CUDA REQUIRED
-                            VERSION_MIN 8.0
-                            PRINT CUDA_INCLUDES)
+                             VERSION_MIN 9.0
+                             RECOMMEND_MIN 11.0
+                             RECOMMEND_MIN_REASON
+                                "We don't actively test CUDA older than 11"
+                             PRINT CUDA_INCLUDES)
         set (CUDA_INCLUDES ${CUDA_TOOLKIT_ROOT_DIR}/include)
         include_directories (BEFORE "${CUDA_INCLUDES}")