[SYCL][NATIVECPU][libclc]Mark opencl_c_generic_address_space as unsupported on Native CPU (#13109)

Similarly to what is done for `nvptx` in
#13015, Native CPU maps `private` and
`generic` to the same address spaces, so we need to avoid getting
multiple definitions for the libclc builtins that use `generic`.

Author: PietroGhg

libclc/CMakeLists.txt

@@ -435,6 +435,8 @@ foreach( t ${LIBCLC_TARGETS_TO_BUILD} )
       set( t "spir64--" )
       set( build_flags "-Wno-unknown-assumption")
       set( opt_flags -O3 )
+    elseif( ${ARCH} STREQUAL "x86_64")
+      set( supports_generic_addrspace FALSE )
     else()
       set( build_flags )
       set( opt_flags -O3 )
@@ -455,6 +457,13 @@ foreach( t ${LIBCLC_TARGETS_TO_BUILD} )
       "+cl_khr_3d_image_writes")
     if(supports_generic_addrspace)
       string( APPEND CL_3_0_EXTENSIONS ",+__opencl_c_generic_address_space" )
+    else()
+      # Explictly disable opencl_c_generic_address_space (it may be enabled
+      # by default on some targets). We also disable opencl_c_pipes and
+      # opencl_c_device_enqueue since they require generic address space.
+      string( APPEND CL_3_0_EXTENSIONS ",-__opencl_c_generic_address_space" )
+      string( APPEND CL_3_0_EXTENSIONS ",-__opencl_c_pipes" )
+      string( APPEND CL_3_0_EXTENSIONS ",-__opencl_c_device_enqueue" )
     endif()
     list( APPEND flags ${CL_3_0_EXTENSIONS})