DEBUG: /usr/bin/x86_64-rosa-linux-gnu-ld: .libs/sample_plugin.o: in function `policy_open':
DEBUG: /builddir/build/BUILD/sudo-1.9.12p2/plugins/sample/./sample_plugin.c:89: undefined reference to `sudo_printf'
DEBUG: /usr/bin/x86_64-rosa-linux-gnu-ld: .libs/sample_plugin.o: in function `io_open':
DEBUG: /builddir/build/BUILD/sudo-1.9.12p2/plugins/sample/./sample_plugin.c:404: undefined reference to `sudo_printf'
plugins/sample is, first of all, built by default despite plugins/sample/README. Also it fails to build with
-Wl,--no-undefined