doc: document Solaris printf bug with large float precisions

doc: document Solaris printf bug with large float precisions

* doc/posix-functions/dprintf.texi (dprintf):
* doc/posix-functions/fprintf.texi (fprintf):
* doc/posix-functions/printf.texi (printf):
* doc/posix-functions/snprintf.texi (snprintf):
* doc/posix-functions/sprintf.texi (sprintf):
* doc/posix-functions/vdprintf.texi (vdprintf):
* doc/posix-functions/vfprintf.texi (vfprintf):
* doc/posix-functions/vprintf.texi (vprintf):
* doc/posix-functions/vsnprintf.texi (vsnprintf):
* doc/posix-functions/vsprintf.texi (vsprintf):
Mention that these functions mishandle large floating point
precisions on Solaris 10.  The same bug is also present in Solaris
8, and I assume earlier.  This causes "cd gnulib-tests; make
check" to fail on Solaris 8 (and I assume, later) when building
the latest coreutils, in test-vasprintf-posix's call to
my_asprintf (&result, "%.4000f %d", 1.0, 99).  I have not checked
the wide flavors (e.g., wprintf) so this patch just updates the
documentation for the narrow ones.