[SYCL] Remove -std=c++14 from tests as new SYCL 2020 features require C++17

[dm-vodopyanov]

This patch removes -std=c++14 from SYCL tests because some of the SYCL
2020 features require C++17 features and syntax

[dm-vodopyanov]

Failures in Jenkins/pre-ci-linux are not related to this patch:

[2021-03-26T19:54:56.078Z] [proxychains] DLL init: proxychains-ng 4.14-git-34-gfa9644d

[2021-03-26T19:54:56.078Z] Abort was called at 87 line in file:
[2021-03-26T19:54:56.078Z] ../neo/shared/source/os_interface/linux/drm_buffer_object.cpp

[dm-vodopyanov]

Failures in Jenkins/pre-ci-windows is not related to the changes in the patch. They can be flaky. With previous run of Jenkins/pre-ci-windows, test regression/kernel_unnamed.cpp failed, now - Sampler/unnormalized-clampedge-nearest.cpp.
@DenisBakhvalov , @kbobrovs and @AlexeySachkov , can you please re-approve?

[dm-vodopyanov]

@vladimirlaz , @bader , can you please merge this PR?

[bader]

Failures in Jenkins/pre-ci-windows is not related to the changes in the patch. They can be flaky. With previous run of Jenkins/pre-ci-windows, test regression/kernel_unnamed.cpp failed, now - Sampler/unnormalized-clampedge-nearest.cpp.
@DenisBakhvalov , @kbobrovs and @AlexeySachkov , can you please re-approve?

Please, address pre-commit checks failure to unblock the merge.
Even though the failure is not related to the patch, you still have to pass all checks.
If you are not able to fix it, you can file an issue to someone else and disable the test in pre-commit validation.

[DenisBakhvalov]

Opened intel/llvm#8814 for SYCL/Sampler tests.

[kbobrovs]

LGTM

[vladimirlaz]

Could you please revert changes in Sampler tests:
@cperkinsintel implemented some WA there:
#207
#196

[dm-vodopyanov]

Didn't revert Sampler/normalized-clamp-nearest.cpp because there were no fixes for this test.