Retire the separate ChangeLog files in nptl/ and nptl_db/ subdirs.
Separate ftell from fseek logic and avoid modifying FILE data (#16532)

ftell semantics are distinct from fseek(SEEK_CUR) especially when it
is called on a file handler that is not yet active.  Due to this
caveat, much care needs to be taken while modifying the handler data
and hence, this first iteration on separating out ftell focusses on
maintaining handler data integrity at all times while it figures out
the current stream offset.  The result is that it makes a syscall for
every offset request.

There is scope for optimizing this by caching offsets when we know
that the handler is active.  A simple way to find out is when the
buffers have data.  It is not so simple to find this out when the
buffer is empty without adding some kind of flag.
Use cached offset in ftell when reliable

The cached offset is reliable to use in ftell when the stream handle
is active.  We can consider a stream as being active when there is
unflushed data.  However, even in this case, we can use the cached
offset only when the stream is not being written to in a+ mode,
because this case may have unflushed data and a stale offset; the
previous read could have sent it off somewhere other than the end of
the file.

There were a couple of adjustments necessary to get this to work.
Firstly, fdopen now ceases to use _IO_attach_fd because it sets the
offset cache to the current file position.  This is not correct
because there could be changes to the file descriptor before the
stream handle is activated, which would not get reflected.

A similar offset caching action is done in _IO_fwide, claiming that
wide streams have 'problems' with the file offsets.  There don't seem
to be any obvious problems with not having the offset cache available,
other than that it will have to be queried in a subsequent
read/write/seek.  I have removed this as well.

The testsuite passes successfully with these changes on x86_64.
Fix up formatting
Fix up formatting in tst-ftell-active-handler.c