Fix malfunction of socket functions on HP-UX in 64-bit mode. * m4/socketlib.m4 (gl_SOCKETLIB): Add comment. * m4/extensions.m4 (AC_USE_SYSTEM_EXTENSIONS): Define _HPUX_ALT_XOPEN_SOCKET_API. * modules/accept (Depends-on): Add 'extensions'. * modules/getpeername (Depends-on): Likewise. * modules/getsockname (Depends-on): Likewise. * modules/getsockopt (Depends-on): Likewise. * modules/recvfrom (Depends-on): Likewise. * doc/posix-functions/accept.texi: Mention the HP-UX socklen_t problem. * doc/posix-functions/getpeername.texi: Likewise. * doc/posix-functions/getsockname.texi: Likewise. * doc/posix-functions/getsockopt.texi: Likewise. * doc/posix-functions/recvfrom.texi: Likewise.

Please create and read the docs with

  $ cd doc
  $ make gnulib.html
  $ xdg-open gnulib.html

or read the online manual at

  https://www.gnu.org/software/gnulib/manual/gnulib.html