[SYCL] Add support for auxiliary triple specification to Frontend

Summary:
Add host predefined macros to compilation for SYCL device, which is
required for pre-processing host specific includes (e.g. system
headers).

Reviewers: ABataev, jdoerfert

Subscribers: ebevhan, Anastasia, cfe-commits, keryell, Naghasan, Fznamznon

Tags: #clang

Differential Revision: https://reviews.llvm.org/D71286



Signed-off-by: Alexey Bader <alexey.bader@intel.com>