[SYCL][test-e2e] Fix how clang++ is called (intel#11785) (intel#18168)

Jira: https://jira.devtools.intel.com/browse/CMPLRLLVM-53056
xmain commit:
[3b97561](intel-restricted/applications.compilers.llvm-project@3b97561)
It was part of a pulldown.

This test called clang++ directly. I think we need to use %clangxx

Thanks

Signed-off-by: Arvind Sudarsanam <[email protected]>

Author: asudarsa

sycl/test-e2e/Basic/spirv_device_obj_smoke.cpp

@@ -1,6 +1,6 @@
 // UNSUPPORTED: cuda || hip
-// RUN: clang++ -fsycl -fsycl-device-obj=spirv -c -o %t.o %s
-// RUN: clang++ -fsycl -o %t.out %t.o
+// RUN: %clangxx -fsycl -fsycl-device-obj=spirv -c -o %t.o %s
+// RUN: %clangxx -fsycl -o %t.out %t.o
 // RUN: %{run} %t.out
 
 // This test verifies SPIR-V based fat objects.