Why fixing 9533 doesn't fix 7744: revealed!

[Paolo Carlini]

Nathan Myers wrote:

>Don't worry, you'll use it for ::recv and its MSG_* flags, and for 
>fstat and fstat64, and for S_ISREG vs S_IFREG.  Lucky you.
>
Be adviced that I will always do my best to avoid using the autoconf
machinery ;)

Seriously, during the weekand I plan to prepare the fix for 7744 (the
simple one, using a flag, to begin with), then get to 9533 and the
delightful autoconf issues...

Now...

Seriously, fstat64 I can probably spare, for now, I think... currently
we don't support large files at all, right?
(there is a long standing PR about this, 8610, which definitely I would
rather address in a couple of months, not now ;)

As regards the other options, could you please help me a bit?

- S_ISREG vs S_IFREG: the first one is Posix, the latter not, I think.
  Probably AC_TRY_COMPILE tests are needed for the first with a fallback
  option for the second, right?

- MSG_* flags: I admit my ignorance: I tried what you suggested on Linux
  and everything worked flawlessly. Where can I find a description of the
  other possibilities?

Thanks,
Paolo.