[Bug libstdc++/81751] __basic_file::sync() may flush _all_ files

[bugzilla.volker at kabelmail dot de]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81751

--- Comment #3 from Volker Wehrs <bugzilla.volker at kabelmail dot de> ---
Why is sync() (alias fflush()) called in sys_open(FILE*,...) at all?

1. It is not called in sys_open(int,...)
2. Both sys_open() functions are called in the constructor of stdio_filebuf
_only_.

So, as __basic_file seem to be intended as an internal class, maybe the call to
sync() can completely be omitted as there definitively is no open file.