Bug#984131: flmsg: ftbfs with GCC-11

[Christoph Berg <myon@debian.org>]

> flmsg.cxx: In function ‘void rotate_log(std::string)’:
> flmsg.cxx:2848:24: error: ‘streampos’ is not a member of ‘std::ostringstream’ {aka ‘std::__cxx11::basic_ostringstream<char>’}
>  2848 |         ostringstream::streampos p;
>       |                        ^~~~~~~~~

For the record, the new upstream version 4.0.19 which I just pushed to
git probably works better with gcc-11, but has problems with xmlrpc:

g++ -DHAVE_CONFIG_H -I.  -I. -I./include -I/usr/include/flxmlrpc -Wdate-time -D_FORTIFY_SOURCE=2 -I/usr/include/cairo -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/pixman-1 -I/usr/include/uuid -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/uuid -I/usr/include/freetype2 -I/usr/include/libpng16 -I/usr/include/cairo -I/usr/include/glib-2.0 -I/usr/lib/x86_64-linux-gnu/glib-2.0/include -I/usr/include/pixman-1 -I/usr/include/uuid -I/usr/include/freetype2 -I/usr/include/libpng16  -I. -I./include   -pipe -Wall -fexceptions -O2 -ffast-math -finline-functions -fomit-frame-pointer   -DNDEBUG -I/usr/include/flxmlrpc -g -O2 -ffile-prefix-map=/srv/projects/afu/flmsg/flmsg=. -fstack-protector-strong -Wformat -Werror=format-security -c -o blank-dnd/flmsg-dnd_tab.o `test -f 'blank-dnd/dnd_tab.cxx' || echo './'`blank-dnd/dnd_tab.cxx
flmsg.cxx: In function ‘int main(int, char**)’:
flmsg.cxx:1927:17: error: ‘set_pname’ is not a member of ‘XmlRpc’
 1927 |         XmlRpc::set_pname(pname);
      |                 ^~~~~~~~~

(I have no plans to fix this since I don't use flmsg.)

Christoph