[SYCL][Driver]Enable multiple third-party targets for SYCL AOT.

[srividya-sundaram]

This patch enables -fsycl-targets option to support a comma-separated list of NVidia and AMD Processor Graphics values as target triple values for the SYCL AOT flow.

Example:

clang++  -###  -fsycl  -fsycl-targets=nvidia_gpu_sm_60,nvidia_gpu_sm_70  syclfile.cpp
clang++  -###  -fsycl  -fsycl-targets=amd_gpu_gfx90a,amd_gpu_gfx90c      syclfile.cpp

[mdtoguchi]

LGTM - are there plans on updating documentation to allow for multiple target support?

[dm-vodopyanov]

From the PR description:

clang++  -###  -fsycl  -fsycl-targets=nvidia_gpu_sm_60, nvidia_gpu_sm_70  syclfile.cpp
clang++  -###  -fsycl  -fsycl-targets=amd_gpu_gfx90a, amd_gpu_gfx90c      syclfile.cpp

I assume there should be no space between values in -fsycl-targets option? If not, please update the description

[srividya-sundaram]

From the PR description:

clang++  -###  -fsycl  -fsycl-targets=nvidia_gpu_sm_60, nvidia_gpu_sm_70  syclfile.cpp
clang++  -###  -fsycl  -fsycl-targets=amd_gpu_gfx90a, amd_gpu_gfx90c      syclfile.cpp

I assume there should be no space between values in -fsycl-targets option? If not, please update the description

I added some extra space for readability purposes but I have removed the spaces now in the description.