Fixes for netdb.h. * m4/netdb_h.m4: Assume that if netdb.h exists, it works. * lib/netdb.in.h: Fix typo. Reported by Bruno Haible <bruno@clisp.org> * lib/netdb.in.h: Include sys/socket.h for platforms without netdb.h, to get structures like hostent on MinGW. * modules/netdb (Depends-on): Add sys_socket.