[SYCL][CMake][MSVC] Fix link.exe /OPT detection (#16811)

CMake's check_linker_flag does no split flags by spaces, so the current
call passes the single option `"/OPT:REF LINKER:/OPT:ICF"` with a space
in it to link.exe. (The first `LINKER:` prefix is parsed). This was also
broken before ede906c ([CMake][MSVC]
Wrap more Linker flags for ICX (#16284)), where it would pass `"/OPT:REF
/OPT:ICF"` as a single option.

This results in the check failing and so the build does not ever enable
these flags, even though they would be supported if the check was
correct.

Use comma as the separator as supported by the `LINKER:` syntax to fix
it.

Author: Maetveis

sycl/CMakeLists.txt

@@ -75,7 +75,7 @@ if(MSVC)
     add_link_options("LINKER:/DEBUG")
 
     # Enable unreferenced removal and ICF in Release mode.
-    check_linker_flag(CXX "LINKER:/OPT:REF LINKER:/OPT:ICF" LINKER_SUPPORTS_OPTS)
+    check_linker_flag(CXX "LINKER:/OPT:REF,/OPT:ICF" LINKER_SUPPORTS_OPTS)
     if (LINKER_SUPPORTS_OPTS AND uppercase_CMAKE_BUILD_TYPE STREQUAL "RELEASE")
       add_link_options("LINKER:/OPT:REF" "LINKER:/OPT:ICF")
     endif()