bug#36342: accept4 detection on illumos needs -lsocket -lnsl

[Michal Nowak <mnowak@startmail.com>]

Hello,

GNU Guile 2.2.5 build fails because accept4 detection on OpenIndiana 
2019.04 (illumos distribution) [1] fails due to "-lsocket -lnsl" not 
being part of the linking process and the build system then tries to 
build it's vendored accept4:

    CC       accept4.lo
In file included from /usr/include/sys/time.h:462:0,
                   from ./sys/time.h:39,
                   from /usr/include/sys/select.h:53,
                   from ./sys/select.h:36,
                   from /usr/include/sys/types.h:640,
                   from ./sys/types.h:28,
                   from ./sys/socket.h:51,
                   from accept4.c:20:
./sys/socket.h:1034:1: error: conflicting types for 'accept4'
   _GL_FUNCDECL_SYS (accept4, int,
   ^
In file included from ./sys/socket.h:58:0,
                   from accept4.c:20:
/usr/include/sys/socket.h:540:12: note: previous declaration of
'accept4' was here
   extern int accept4(int, struct sockaddr *_RESTRICT_KYWD, Psocklen_t, 
int);
              ^~~~~~~
accept4.c:32:1: error: conflicting types for 'accept4'
   accept4 (int sockfd, struct sockaddr *addr, socklen_t *addrlen, int 
flags)
   ^~~~~~~
In file included from ./sys/socket.h:58:0,
                   from accept4.c:20:
/usr/include/sys/socket.h:540:12: note: previous declaration of
'accept4' was here
   extern int accept4(int, struct sockaddr *_RESTRICT_KYWD, Psocklen_t, 
int);
              ^~~~~~~

This is fixed by LIBS="-lsocket -lnsl" in the build environment.

This was in the past reported both on the guile-user [2] and 
openindiana-discuss [3] mailing lists, where you also can see the build 
error in full.

Thanks,
Michal

[1] https://illumos.org/man/3socket/accept4
[2] https://lists.gnu.org/archive/html/guile-user/2018-03/msg00006.html
[3] 
https://openindiana.org/pipermail/openindiana-discuss/2018-March/021931.html