Fix builds with DJGPP

Fix builds with DJGPP

CLA: trivial

To get the master branch compiled with DJGPP some minor
adjustments are required. They will have no impact on any other ports.
The DJGPP port uses the Watt-32 library to provide the required network
functionality and some of its headers need to be included.

Neither DJGPP nor the Watt-32 library provide in_addr_t thus it must be
provided as it is done for OPENSSL_SYS_WINDOWS in crypto/bio/b_addr.c.

In the DJGPP section of include/internal/sockets.h the following Watt-32
headers must be added:

  -  arpa/inet.h: to provide declaration of inet_ntoa required in crypto/bio/b_addr.c
  -  netinet/tcp.h: to provide defintion of TCP_NODELAY required in crypto/bio/b_sock2.c

Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Tomas Mraz <tomas@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/17623)