__readfn and __writefn parameter to match new definition of
FILE's _read and _write methods.
(_funopen_r): Ditto.
(funopen): Ditto.
(_funopen_r): Ditto.
* libc/include/sys/config.h (_READ_WRITE_BUFSIZE_TYPE) Define
as type int if not already defined. Add comment to explain.
* libc/include/sys/reent.h: Include stddef.h.
(struct __sFILE): Change type of last parameter in declaration
of _read and _write methods to _READ_WRITE_BUFSIZE_TYPE.
(struct __sFILE64): Ditto.
* libc/stdio/local.h (__sread): Declare with last parameter set
to _READ_WRITE_BUFSIZE_TYPE.
(__seofread): Ditto.
(__swrite): Ditto.
(__swrite64): Ditto.
* libc/stdio/fvwrite.c (__sfvwrite_r): Change type of local
variables w and s to _READ_WRITE_RETURN_TYPE.
* libc/stdio/fflush.c (__sflush_r): Change type of local variables
n and t to _READ_WRITE_BUFSIZE_TYPE and _READ_WRITE_RETURN_TYPE.
Add local variables flags to keep _flags value.
* libc/stdio/fmemopen.c (fmemreader): Align to above change.
(fmemwriter): Ditto.
* libc/stdio/fopencookie.c (fcreader): Ditto.
(fcwriter): Ditto.
* libc/stdio/funopen.c (funread): Ditto.
(funwrite): Ditto.
(funreader): Ditto.
(funwriter): Ditto.
* libc/stdio/open_memstream.c (memwriter): Ditto.
* libc/stdio/stdio.c (__sread): Ditto.
(__seofread): Ditto.
(__swrite): Ditto.
* libc/stdio64/stdio64.c (__swrite64): Ditto.