[Bug libstdc++/63746] i/o fragmentation inside basic_filebuf::xsputn

[pluto at agmk dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=63746

--- Comment #1 from Pawel Sikora <pluto at agmk dot net> ---
Created attachment 33893
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=33893&action=edit
my hack.