Legacy _IO_* symbols and Flaot128 transition

[Florian Weimer]

libio exports a bunch of symbols for historic reasons:

_IO_fprintf
_IO_printf
_IO_sprintf
_IO_sscanf
_IO_vfprintf
_IO_vfscanf
_IO_vsprintf

These aren't compat symbols yet, but will not be in installed headers 
for glibc 2.28.  Zack's cleanup patches only turns _IO_vfscanf into a 
compat symbol (in “Add __vfscanf_internal and __vfwscanf_internal with 
flags arguments.”).

I think we should turn all of them into compat symbols and drop their 
compatibility wrappers from nldbl_nonshared.a, and avoid adding 
binary128 compatibility wrappers for them.

I can work on a patch if that would help.

Comments?

Thanks,
Florian