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

[pawel_sikora at zoho dot com]

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

Pawel Sikora <pawel_sikora at zoho dot com> changed:

           What    |Removed                     |Added
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      Known to fail|                            |4.9.2, 5.4.1, 6.2.1

--- Comment #2 from Pawel Sikora <pawel_sikora at zoho dot com> ---
ping. could you review/apply attached trivial patch?