Minor build fixes in cmake

[VileLasagna]

Three minor cmake fixes in hipsycl itself:

1 - Explicitly set CMAKE_CXX_STANDARD to 14, in case it doesn't get automagically set

2 - Set and forwarded CMAKE_CUDA_HOST_COMPILER and CMAKE_CUDA_STANDARD to the CUDA target if building with NVCC, as those don't always get correctly inherited to match the C++ side of the build

3 - Probed the system for the ROCM_PATH variable and used it, if present, to add ROCM's include path to the build. I myself had always been adding the full path manually, but ROCM sets this on a file in profile.d when it install itself, so probing this env variable is an option

None of these changes should break pre-existing builds. The one that could would be no1 if the compiler doesn't support it but it seems to me SYCL doesn't even build with a standard lower than 14 due to lambda shenanigans

[illuhad]

Thank you! :) However, it seems that this PR breaks the Travis CI build (at least with clang-cuda), interestingly with the same error as reported in #50. I've just rechecked and it builds fine without this PR. Could you please investigate? Does this PR depend on PR #40 ?

[VileLasagna]

It should build straight off of current master. Can you give me the console output of your CI so I can have a look?

[illuhad]

See here. For testing, you can use the Dockerfiles or singularity definition files in install (replace repository with your fork and checkout your branch), as the CI just tries to build those.

[VileLasagna]

That's interesting. I run into this specific issue myself quite a bit with clang and nvcc. The workaround is to pass -D__STRICT_ANSI__ into CXX_FLAGS. Curious it showed up only now in that build. I'll have a play but my guess is that the culprit would be me enforcing CXX_STD to 14. If it just works otherwise in CI I might just revert that one commit.

[VileLasagna]

It indeed was the CXX standard... kind of curious that it seemed I bumped into needing it on my side. Good to come in contact with the docker stuff to check before pushing though. I've just pushed a revert commit but can, if you'd prefer to have a cleaner tree, do some evil rebasing trickery and get rid of the commit(s) altogether

[psalz]

Without having looked at the CI output our tried building this myself, it might be due to CMake defaulting to GNU standards (i.e., gnu++14) on Linux. Try setting set_property(TARGET <target> PROPERTY CXX_EXTENSIONS OFF) - at least that's what I previously had to do for a similar sounding issue.

[illuhad]

Thanks for all the ideas. I think we should try getting C++14 enabled by default because of the feedback from issue #56, where a missing -std=c++14 caused compilation failures. @VileLasagna, could you please have a look at @psalz's proposals?

[VileLasagna]

Sure thing. Will try and massage that into conformity