synergy: update to 1.12.0

Bug fixes:
    #6748 Copyright year in about dialog isn't updated
    #6730 Updating synergy looses settings
    #6734 Fixed naming of installers for linux and windows
    #6487 Mouse freezes or key repeats on Linux client
    #6663 Limit GUI log Window to prevent it using up too much RAM over time
    #6587 Auto config setting doesn't do anything
    #6620 Unit tests are no longer built
    #6670 Build computers failing with language file error
    #6661 Removed deprecated namespace in gtest/gmock by updating
    #6601 Update man page with missing crypto option
    #4036 Client cursor constrained to old resolution
    #6716 Denial of Service vulnerability on servers with 4GB of ram or less
Enhancements:
    #6739 Add submodules cloning to cmake
    #6736 Command line option for custom TLS Certificate
    #6666 Add doxygen documentation output from pipelines
    #6715 Updated language file from Crowdin
    #6722 Allow servers to be announced by screen name instead of IP
    #6720 Add macqtdeploy to cmake
    #6725 Disable the building of tests with CMake option
Features:
    #6538 System-wide config for all system users

(tnn)