Enable LTO optimisations
    
    This change enable gcc LTO optimisations.

    It helps reduce RAM usege and rpms size.

    

    For example on F31 octave rpm with LTO 17MB vs 18MB without LTO.

    And octave-debuginfo rpm with LTO 117MB vs 128MB without LTO.

    

    Enabling it has no any issue in runtime but can take some more time to build (but not critical).