[SYCL] Add identification macro for DPCPP compiler

[elizabethandrews]

Add predefined macro __DPCPP_COMPILER = 1, to uniquely identify DPCPP compiler.

Signed-off-by: Elizabeth Andrews elizabeth.andrews@intel.com

[AaronBallman]

On the assumption that we don't need the feature-testing components because it will be handled through other means, this LGTM

[premanandrao]

LGTM, thanks for the review @AaronBallman

[elizabethandrews]

Thanks @AaronBallman and @premanandrao!

@pvchupin is there a known failure with pre-commit testing? There is a stream test failing. I do not know how this change can cause it.

[premanandrao]

@pvchupin is there a known failure with pre-commit testing? There is a stream test failing. I do not know how this change can cause it.

@pvchupin thinks it is a flaky failure, in #2967

[pvchupin]

Let's discuss more on this macro first.

[bader]

Let's discuss more on this macro first.

Any updates on this?

[elizabethandrews]

Let's discuss more on this macro first.

Any updates on this?

After an offline discussion with @pvchupin and others, a decision was made to not support any additional macros at the moment. SYCL_LANGUAGE_VERSION can be used to identify any SYCL compiler.