Same issue. I've changed to building in a cowbuilder chroot to exclude host issues. Also excluded it being a full disk issue.
kmk_builtin_append -n "/home/user/whonix_binary/temp_packages_virtualbox/virtualbox-6.1.0-dfsg/out/obj/UICommon/gen/qtrcc/VirtualBox2_x3.gen.o.dep" "" "/home/user/whonix_binary/temp_packages_virtualbox/virtualbox-6.1.0-dfsg/out/obj/UICommon/qtrcc/VirtualBox2_x3.gen.cpp:" "" kmk: *** Exiting with status 2 make[1]: *** [debian/rules:64: override_dh_auto_build] Error 2 make[1]: Leaving directory '/home/user/whonix_binary/temp_packages_virtualbox/virtualbox-6.1.0-dfsg' make: *** [debian/rules:39: build] Error 2 dpkg-buildpackage: error: debian/rules build subprocess returned exit status 2 kmk_builtin_append -n "/home/user/whonix_binary/temp_packages_virtualbox/virtualbox-6.1.0-dfsg/out/obj/UICommon/gen/qtrcc/VirtualBox2_x4.gen.o.dep" "" "/home/user/whonix_binary/temp_packages_virtualbox/virtualbox-6.1.0-dfsg/out/obj/UICommon/qtrcc/VirtualBox2_x4.gen.cpp:" "" kmk_builtin_append -n "/home/user/whonix_binary/temp_packages_virtualbox/virtualbox-6.1.0-dfsg/out/obj/UICommon/gen/qtrcc/VirtualBox2_x2.gen.o.dep" "" "/home/user/whonix_binary/temp_packages_virtualbox/virtualbox-6.1.0-dfsg/out/obj/UICommon/qtrcc/VirtualBox2_x2.gen.cpp:" ""
