OvmfPkg: Add XCODE5 statements to fix build break
    
    https://bugzilla.tianocore.org/show_bug.cgi?id=559
    
    The XCODE5 tool chain has a FAMILY of GCC.  The
    GCC statements in the [BuildOptions] section add
    flags that are not compatible with XCODE5.  Add
    empty XCODE5 statements in [BuildOptions] sections
    to prevent the use of the GCC flags in XCODE5
    builds.
    
    Cc: Laszlo Ersek <lersek@redhat.com>
    Cc: Andrew Fish <afish@apple.com>
    Contributed-under: TianoCore Contribution Agreement 1.0
    Signed-off-by: Michael D Kinney <michael.d.kinney@intel.com>
    Reviewed-by: Laszlo Ersek <lersek@redhat.com>