[SYCL] Return back c++17 option to the test

[romanovvlad]

It seems that without -fsycl the default version of c++ is less than c++17 which is required for SYCL headers.

[pvchupin]

That's very strange because community switched to C++17 by default and we should have already this change pulled down from upstream. We need to follow up on the current default.
@mdtoguchi, can you comment please?

[pvchupin]

That's very strange because community switched to C++17 by default and we should have already this change pulled down from upstream. We need to follow up on the current default. @mdtoguchi, can you comment please?

On the other hand... probably that was for Linux only?
llvm/llvm-project@e321c8d

[mdtoguchi]

Looks like linux based targets only:

sycl-run:1197> clang++ -target x86_64-unknown-windows-msvc -xc++ -E -dM /dev/null | grep plusplus
#define __cplusplus 201402L
sycl-run:1198> clang++ -target x86_64-unknown-linux-gnu -xc++ -E -dM /dev/null | grep plusplus
#define __cplusplus 201703L