[SYCL] Fix SYCL unittest CMake (#7489)

a11cd0d moved gtest to another
directory which causes the SYCL CMake to not find it and effectively
skip configuring the unittests entirely. This commit adjusts the gtest
search in accordance with the new location.

Signed-off-by: Larsen, Steffen <steffen.larsen@intel.com>

Author: steffenlarsen

sycl/CMakeLists.txt

@@ -336,7 +336,7 @@ if(SYCL_INCLUDE_TESTS)
       message(FATAL_ERROR
         "Can't build SYCL tests without LLVM_INCLUDE_TESTS enabled.")
   endif()
-  if(EXISTS ${LLVM_MAIN_SRC_DIR}/utils/unittest/googletest/include/gtest/gtest.h)
+  if(EXISTS ${LLVM_THIRD_PARTY_DIR}/unittest/googletest/include/gtest/gtest.h)
     add_subdirectory(unittests)
     list(APPEND SYCL_TEST_DEPS SYCLUnitTests)
   endif()