Implement getaddrinfo fallback for MS-Windows

See http://lists.gnu.org/archive/html/emacs-devel/2016-02/msg01602.html
for more details.

* nt/mingw-cfg.site (ac_cv_func_getaddrinfo)
(ac_cv_func_gai_strerror): Set to "yes", as the configure script's
test program is not smart enough to auto-detect these.
* nt/inc/sys/socket.h (getaddrinfo, freeaddrinfo): Redirect to
sys_getaddrinfo and sys_freeaddrinfo.  Provide prototypes for
sys_getaddrinfo and sys_freeaddrinfo.

* src/w32.c (init_winsock): Try loading getaddrinfo and
freeaddrinfo from ws2_32.dll.
(sys_getaddrinfo, sys_freeaddrinfo): New functions.

* lib-src/pop.c [WINDOWSNT]: Include winsock2.h, not winsock.h,
and also ws2tcpip.h.
(getaddrinfo, freeaddrinfo) [WINDOWSNT]: Redirect to
sys_getaddrinfo and sys_freeaddrinfo, respectively.
(load_ws2, sys_getaddrinfo, sys_freeaddrinfo) [WINDOWSNT]: New
functions.

2 files changed, 9 insertions, 0 deletions

diff --git a/nt/inc/sys/socket.h b/nt/inc/sys/socket.h
index d7ed92d6158..2c72a78b0f4 100644
--- a/nt/inc/sys/socket.h
+++ b/nt/inc/sys/socket.h
@@ -98,6 +98,8 @@ typedef unsigned short uint16_t;
 #define accept         sys_accept
 #define recvfrom       sys_recvfrom
 #define sendto         sys_sendto
+#define getaddrinfo    sys_getaddrinfo
+#define freeaddrinfo   sys_freeaddrinfo
 
 int sys_socket(int af, int type, int protocol);
 int sys_bind (int s, const struct sockaddr *addr, int namelen);
@@ -118,6 +120,9 @@ int sys_recvfrom (int s, char *buf, int len, int flags,
                   struct sockaddr *from, int * fromlen);
 int sys_sendto (int s, const char * buf, int len, int flags,
                 const struct sockaddr *to, int tolen);
+int sys_getaddrinfo (const char * node, const char * service,
+                     const struct addrinfo * hints, struct addrinfo ** res);
+void sys_freeaddrinfo (struct addrinfo * ai);
 
 /* In addition to wrappers for the winsock functions, we also provide
    an fcntl function, for setting sockets to non-blocking mode.  */
diff --git a/nt/mingw-cfg.site b/nt/mingw-cfg.site
index 05034fedd48..ff9df60c275 100644
--- a/nt/mingw-cfg.site
+++ b/nt/mingw-cfg.site
@@ -68,6 +68,10 @@ ac_cv_func_getsockname=yes
 ac_cv_func_getpeername=yes
 # Implemented as sys_socket in w32.c
 ac_cv_func_socket=yes
+# Implemented as sys_getaddrinfo in w32.c
+ac_cv_func_getaddrinfo=yes
+# Implemented as an inline function in ws2tcpip.h
+ac_cv_func_gai_strerror=yes
 # Implemented in w32.c
 ac_cv_func_mkostemp=yes
 ac_cv_func_readlink=yes