BaseTools:build failure in CLANGPDB tool chain
    
    REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2520
    
    Incremental build failure in CLANGPDB tool chain on Windows host
    The build failure is like below when do incremental build.
    The root cause is in generated deps_target file. It has one line ":".
    
    Signed-off-by: Zhiju.Fan <zhijux.fan@intel.com>
    
    Cc: Liming Gao <liming.gao@intel.com>
    Cc: Bob Feng <bob.c.feng@intel.com>
    Reviewed-by: Bob Feng <bob.c.feng@intel.com>