+ SYS_SOCKET_H='sys/socket.h'
+ fi
+ if test -n "$SYS_SOCKET_H"; then
+ dnl Check prerequisites of the <sys/socket.h> replacement.
+ gl_CHECK_NEXT_HEADERS([sys/socket.h])
+ if test $ac_cv_header_sys_socket_h = yes; then
+ HAVE_SYS_SOCKET_H=1
+ HAVE_WS2TCPIP_H=0
+ else
+ HAVE_SYS_SOCKET_H=0
+ dnl We cannot use AC_CHECK_HEADERS_ONCE here, because that would make
+ dnl the check for those headers unconditional; yet cygwin reports
+ dnl that the headers are present but cannot be compiled (since on
+ dnl cygwin, all socket information should come from sys/socket.h).
+ AC_CHECK_HEADERS([ws2tcpip.h])
+ if test $ac_cv_header_ws2tcpip_h = yes; then
+ HAVE_WS2TCPIP_H=1
+ else
+ HAVE_WS2TCPIP_H=0
+ fi
+ fi
+ gl_PREREQ_SYS_H_WINSOCK2
+ AC_SUBST([HAVE_SYS_SOCKET_H])
+ AC_SUBST([HAVE_WS2TCPIP_H])
+ fi
+ AC_SUBST([SYS_SOCKET_H])
+])
+
+# Common prerequisites of of the <sys/socket.h> replacement and of the
+# <sys/select.h> replacement.
+# Sets and substitutes HAVE_WINSOCK2_H.
+AC_DEFUN([gl_PREREQ_SYS_H_WINSOCK2],
+[
+ m4_ifdef([gl_UNISTD_H_DEFAULTS], [AC_REQUIRE([gl_UNISTD_H_DEFAULTS])])
+ m4_ifdef([gl_SYS_IOCTL_H_DEFAULTS], [AC_REQUIRE([gl_SYS_IOCTL_H_DEFAULTS])])
+ AC_CHECK_HEADERS_ONCE([sys/socket.h])
+ if test $ac_cv_header_sys_socket_h != yes; then