doc: update for Solaris 11.3

[Bruno Haible]

The latest gnulib doc update for Solaris was for Solaris 11 2011-11, which
according to Wikipedia [1] and the 'uname -a' output is Solaris 11.0.
Quite a long time ago, and Solaris 11.3 is probably the final Solaris release 
[2].
Therefore let me update the gnulib doc.

Here are the diffs:
http://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=2464dbce67a0693b5fbe21cd5588bc1f21b8ff25
http://git.savannah.gnu.org/gitweb/?p=gnulib.git;a=commitdiff;h=d00ddf69fbd36a8159030682d6c1153448ff6f30

As usual, the interesting part is which bugs have been fixed in Solaris 11.3.
Very few:
$ fgrep -rl 'Solaris 11.0' doc/ | sort
doc/glibc-functions/asprintf.texi
doc/glibc-functions/getgrouplist.texi
doc/glibc-functions/obstack_printf.texi
doc/glibc-functions/obstack_vprintf.texi
doc/glibc-functions/pthread_getname_np.texi
doc/glibc-functions/pthread_setname_np.texi
doc/glibc-functions/pthread_sigqueue.texi
doc/glibc-functions/tdestroy.texi
doc/glibc-functions/vasprintf.texi
doc/posix-functions/fprintf.texi
doc/posix-functions/log.texi
doc/posix-functions/log10.texi
doc/posix-functions/logb.texi
doc/posix-functions/logbf.texi
doc/posix-functions/logbl.texi
doc/posix-functions/printf.texi
doc/posix-functions/signbit.texi
doc/posix-functions/snprintf.texi
doc/posix-functions/sprintf.texi
doc/posix-functions/strncat.texi
doc/posix-functions/strtod.texi
doc/posix-functions/vfprintf.texi
doc/posix-functions/vprintf.texi
doc/posix-functions/vsnprintf.texi
doc/posix-functions/vsprintf.texi
doc/posix-headers/stddef.texi

[1] https://en.wikipedia.org/wiki/Solaris_(operating_system)#Version_history
[2] https://www.theregister.co.uk/2017/09/04/oracle_layoffs_solaris_sparc_teams/