Fix all warnings and remove -Wno-unused-but-set cflag

src/CMakeLists.txt

src/client.h

src/clientiface.cpp

src/clientmap.cpp

src/connection.cpp

src/content_sao.cpp

src/drawscene.cpp

src/environment.h

src/guiEngine.cpp

src/jthread/pthread/jthread.cpp

src/localplayer.cpp

src/map.cpp

src/mapblock.cpp

src/mapgen.cpp

src/mapgen_v6.cpp

src/script/lua_api/l_mainmenu.cpp

src/script/lua_api/l_mapgen.h