xemc: fix constness warnings
xemc: fix constness warnings

since the Xt and Xaw libraries are unlikely to ever be const-corrected,
employ casts at the boundary of the library to silence warnings when
there's no other solution.

ArcEye/machinekit-testing,cdsteinkuehler/MachineKit,ianmcmahon/linuxcnc-mirror,unseenlaser/machinekit,EqAfrica/machinekit,jaguarcat79/ILC-with-LinuxCNC,bmwiedemann/linuxcnc-mirror,cdsteinkuehler/linuxcnc,araisrobo/machinekit,cdsteinkuehler/linuxcnc,Cid427/machinekit,kinsamanka/machinekit,strahlex/machinekit,araisrobo/linuxcnc,cnc-club/linuxcnc,unseenlaser/machinekit,kinsamanka/machinekit,jaguarcat79/ILC-with-LinuxCNC,strahlex/machinekit,aschiffler/linuxcnc,ArcEye/MK-Qt5,unseenlaser/machinekit,cdsteinkuehler/MachineKit,jaguarcat79/ILC-with-LinuxCNC,unseenlaser/machinekit,mhaberler/machinekit,ArcEye/MK-Qt5,unseenlaser/machinekit,ianmcmahon/linuxcnc-mirror,cnc-club/linuxcnc,ArcEye/MK-Qt5,narogon/linuxcnc,ianmcmahon/linuxcnc-mirror,mhaberler/machinekit,narogon/linuxcnc,araisrobo/linuxcnc,araisrobo/machinekit,kinsamanka/machinekit,ianmcmahon/linuxcnc-mirror,unseenlaser/linuxcnc,strahlex/machinekit,RunningLight/machinekit,mhaberler/machinekit,araisrobo/machinekit,unseenlaser/linuxcnc,bobvanderlinden/machinekit,kinsamanka/machinekit,cdsteinkuehler/MachineKit,RunningLight/machinekit,bmwiedemann/linuxcnc-mirror,mhaberler/machinekit,unseenlaser/machinekit,araisrobo/machinekit,ianmcmahon/linuxcnc-mirror,ikcalB/linuxcnc-mirror,bmwiedemann/linuxcnc-mirror,kinsamanka/machinekit,bobvanderlinden/machinekit,ArcEye/machinekit-testing,EqAfrica/machinekit,bobvanderlinden/machinekit,mhaberler/machinekit,ArcEye/MK-Qt5,ArcEye/machinekit-testing,bobvanderlinden/machinekit,araisrobo/machinekit,Cid427/machinekit,ikcalB/linuxcnc-mirror,mhaberler/machinekit,ikcalB/linuxcnc-mirror,aschiffler/linuxcnc,ikcalB/linuxcnc-mirror,unseenlaser/machinekit,narogon/linuxcnc,kinsamanka/machinekit,araisrobo/machinekit,RunningLight/machinekit,unseenlaser/linuxcnc,EqAfrica/machinekit,ArcEye/machinekit-testing,jaguarcat79/ILC-with-LinuxCNC,mhaberler/machinekit,ArcEye/MK-Qt5,cdsteinkuehler/linuxcnc,EqAfrica/machinekit,ikcalB/linuxcnc-mirror,mhaberler/machinekit,Cid427/machinekit,Cid427/machinekit,araisrobo/linuxcnc,bmwiedemann/linuxcnc-mirror,RunningLight/machinekit,cnc-club/linuxcnc,strahlex/machinekit,ikcalB/linuxcnc-mirror,ArcEye/MK-Qt5,bobvanderlinden/machinekit,araisrobo/machinekit,unseenlaser/linuxcnc,RunningLight/machinekit,aschiffler/linuxcnc,bmwiedemann/linuxcnc-mirror,bobvanderlinden/machinekit,RunningLight/machinekit,ArcEye/machinekit-testing,cnc-club/linuxcnc,Cid427/machinekit,strahlex/machinekit,bobvanderlinden/machinekit,narogon/linuxcnc,ArcEye/machinekit-testing,cdsteinkuehler/MachineKit,Cid427/machinekit,cdsteinkuehler/MachineKit,cnc-club/linuxcnc,RunningLight/machinekit,cdsteinkuehler/MachineKit,ikcalB/linuxcnc-mirror,RunningLight/machinekit,kinsamanka/machinekit,ianmcmahon/linuxcnc-mirror,cnc-club/linuxcnc,Cid427/machinekit,araisrobo/linuxcnc,strahlex/machinekit,unseenlaser/machinekit,cdsteinkuehler/linuxcnc,araisrobo/linuxcnc,ArcEye/machinekit-testing,araisrobo/machinekit,narogon/linuxcnc,EqAfrica/machinekit,EqAfrica/machinekit,bobvanderlinden/machinekit,ianmcmahon/linuxcnc-mirror,aschiffler/linuxcnc,araisrobo/machinekit,kinsamanka/machinekit,ArcEye/MK-Qt5,Cid427/machinekit,EqAfrica/machinekit,ArcEye/MK-Qt5,bmwiedemann/linuxcnc-mirror,unseenlaser/linuxcnc,cnc-club/linuxcnc,bmwiedemann/linuxcnc-mirror,EqAfrica/machinekit,strahlex/machinekit,aschiffler/linuxcnc,jaguarcat79/ILC-with-LinuxCNC,ArcEye/machinekit-testing,cdsteinkuehler/linuxcnc,cdsteinkuehler/linuxcnc