configure: add a special case to test for BSD sockets for mingw.

(Patch by Adrien Nader!)

I tried to use "hasgot" to test it but proved too difficult since you
must #include <winsock2.h> to make link succeed (windows magic) which
then makes gcc complain about the prototype being wrong.

Since windows already needs a special case in order to add -lws2_32 and
since we know for sure it will be available, skip the hasgot test and
check $target directly.
configure: add a special case to test for BSD sockets for mingw.

git-svn-id: http://caml.inria.fr/svn/ocaml/trunk@13855 f963ae5c-01c2-4b8c-9fe0-0dff7051ff02

configure

@@ -1054,6 +1054,15 @@ elif sh ./hasgot -lnsl -lsocket socket socketpair bind listen accept connect; th
   cclibs="$cclibs -lnsl -lsocket"
   echo "#define HAS_SOCKETS" >> s.h
   has_sockets=yes
+else
+  case "$target" in
+    *-*-mingw*)
+      inf "You have BSD sockets (with libraries '-lws2_32')"
+      cclibs="$cclibs -lws2_32"
+      echo "#define HAS_SOCKETS" >> s.h
+      has_sockets=yes ;;
+    *) ;;
+  esac
 fi
 
 if sh ./hasgot -i sys/socket.h -t socklen_t; then