Fails to build with C++14

[steffenlarsen]

Describe the bug
Building with DPC++ with C++14 causes errors. Looks like 4524a6b broke C++14 support and the only test that used it was removed shortly after: 815b43b

Among other similar errors, the commands results in the error:

.../include/sycl/CL/sycl/kernel_handler.hpp:51:13: error: 'auto' not allowed in template parameter until C++17
  template <auto &S, typename T = std::remove_reference_t<decltype(S)>,
            ^~~~
.../include/sycl/CL/sycl/kernel_handler.hpp:52:35: error: no template named 'is_fundamental_v' in namespace 'std'; did you mean 'is_fundamental'?
            std::enable_if_t<std::is_fundamental_v<T>> * = nullptr>
                             ~~~~~^
.../include/c++/7/type_traits:593:12: note: 'is_fundamental' declared here
    struct is_fundamental
           ^

Has C++14 support been dropped in its entirety?

To Reproduce
Build benchmark by running:

git clone https://gitlab.com/NERSC/nersc-proxies/su3_bench.git
cd su3_bench
make -f Makefile.dpcpp USE_SYCL=1 CC=path/to/clang++

Environment:

• OS: Linux
• Device: NVIDIA GPU
• DPC++ version: 77d4fdf

[dm-vodopyanov]

Hi @steffenlarsen, that's correct, since 4524a6b the compiler now supports C++17 and higher C++ standards. I've prepared a PR with an update to documentation: #3478

[steffenlarsen]

According to the documentation (even after the current change in #3478):

• DPC++ runtime and headers require C++14 at least.

However, the failure above stems from CL/sycl/kernel_handler.hpp using C++17 features, so it does not adhere to that requirement. Maybe that point needs to be change accordingly?

[pvchupin]

@steffenlarsen, any concerns if we move forward with #3447 ?

[steffenlarsen]

Apart from my comment above, if this is the plan I will not stand in the way. Thank you for clarifying. 😄