vmm_clock: only build for x86 kernels

ZHF:#199919

pkgs/os-specific/linux/vmm_clock/default.nix

···
     homepage = "https://github.com/voutilad/vmm_clock";
     license = licenses.gpl2;
     maintainers = with maintainers; [ qbit ];
-    platforms = platforms.linux;
+    platforms = [ "i686-linux" "x86_64-linux" ];
   };
 
   enableParallelBuilding = true;