On raspberry pi gcc has version 6.3.0 20170516 (Raspbian 6.3.0-18+rpi1+deb9u1)
and flags -Wrestrict -Wduplicated-branches -Wstringop-overflow=4 are not recognized.

gcc: error: unrecognized command line option ‘-Wduplicated-branches’; did you mean ‘-Wduplicated-cond’?
gcc: error: unrecognized command line option ‘-Wrestrict’; did you mean ‘-mrestrict-it’?
gcc: error: unrecognized command line option ‘-Wstringop-overflow=4’; did you mean ‘-Wstrict-overflow=’?