build: Check for libsocket

On Solaris the socket functions are not found on libc but on libsocket.
We need those for start-stop-daemon.

configure.ac

@@ -97,6 +97,7 @@ AS_IF([test "x$build_dselect" = "xyes"], [
   DPKG_LIB_CURSES
 ])
 AS_IF([test "x$build_start_stop_daemon" = "xyes"], [
+  DPKG_LIB_SOCKET
   DPKG_LIB_PS
   DPKG_LIB_KVM
 ])
@@ -276,6 +277,7 @@ Configuration:
     dselect . . . . . . . . . . . : $build_dselect
 
   System Libraries:
+    libsocket . . . . . . . . . . : ${have_libsocket:-no}
     libps . . . . . . . . . . . . : ${have_libps:-no}
     libkvm  . . . . . . . . . . . : ${have_libkvm:-no}
     libselinux  . . . . . . . . . : $have_libselinux

m4/dpkg-libs.m4

@@ -171,6 +171,23 @@ AC_DEFUN([DPKG_LIB_CURSES], [
   have_libcurses=yes
 ])# DPKG_LIB_CURSES
 
+# DPKG_LIB_SOCKET
+# ---------------
+# Check for socket library
+AC_DEFUN([DPKG_LIB_SOCKET], [
+  AC_ARG_VAR([SOCKET_LIBS], [linker flags for socket library])dnl
+  have_libsocket="no"
+  dpkg_save_libsocket_LIBS=$LIBS
+  AC_SEARCH_LIBS([bind], [socket])
+  LIBS=$dpkg_save_libsocket_LIBS
+  AS_IF([test "x$ac_cv_search_bind" = "xnone required"], [
+    have_libsocket="builtin"
+  ], [test "x$ac_cv_search_bind" != "xno"], [
+    have_libsocket="yes"
+    SOCKET_LIBS="$ac_cv_search_bind"
+  ])
+])# DPKG_LIB_SOCKET
+
 # DPKG_LIB_PS
 # -----------
 # Check for GNU/Hurd ps library

utils/Makefile.am

@@ -63,6 +63,7 @@ start_stop_daemon_SOURCES = \
 
 start_stop_daemon_LDADD = \
 	../lib/compat/libcompat.la \
+	$(SOCKET_LIBS) \
 	$(PS_LIBS) \
 	$(KVM_LIBS) \
 	$(nil)