Use make --output-sync feature when available (bsc#1012422).
    
    The mesages in make output can interleave making it impossible to
    extract warnings reliably. Since version 4 GNU Make supports
    --output-sync flag that prints output of each sub-command atomically
    preventing this issue. Detect the flag and use it if available.
    
    SLE11 has make 3.81 so it is required to include make 4 in the kernel
    OBS projects to take advantege of this.