inet_ntop, inet_pton: forward-compatibility with newer Windows versions

[Bruno Haible]

The functions inet_ntop and inet_pton exist in Windows Vista or newer:
https://docs.microsoft.com/en-us/windows/desktop/api/ws2tcpip/nf-ws2tcpip-inet_ntop
https://docs.microsoft.com/en-us/windows/desktop/api/ws2tcpip/nf-ws2tcpip-inet_pton

So far, gnulib tests whether they are declared. Which, on mingw, by default
is not the case. So, there is the possibility of a conflict at the linker level.

I don't think a linker error would probably be seen, because the function
from Windows is in libws2_32.dll, whereas the function from gnulib is in
libgnu.a. But it is possible that a program that #includes <ws2tcpip.h>
instead of <arpa/inet.h> ends up calling gnulib's function with the wrong
calling convention (stdcall), which will likely lead to a crash.

This patch fixes it. It renames the gnulib function, by adding an 'rpl_' prefix,
thus avoiding any possible conflict.


2019-06-30  Bruno Haible  <address@hidden>

        inet_ntop, inet_pton: Forward-compatibility with newer Windows versions.
        * m4/inet_ntop.m4 (gl_FUNC_INET_NTOP): On native Windows, set
        REPLACE_INET_NTOP to 1 always.
        * m4/inet_pton.m4 (gl_FUNC_INET_PTON): On native Windows, set
        REPLACE_INET_PTON to 1 always.

diff --git a/m4/inet_ntop.m4 b/m4/inet_ntop.m4
index 3804e88..d71246b 100644
--- a/m4/inet_ntop.m4
+++ b/m4/inet_ntop.m4
@@ -1,4 +1,4 @@
-# inet_ntop.m4 serial 20
+# inet_ntop.m4 serial 21
 dnl Copyright (C) 2005-2006, 2008-2019 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -24,15 +24,16 @@ AC_DEFUN([gl_FUNC_INET_NTOP],
   INET_NTOP_LIB=
   gl_PREREQ_SYS_H_WINSOCK2
   if test $HAVE_WINSOCK2_H = 1; then
+    dnl It needs to be overridden, because the stdcall calling convention
+    dnl is not compliant with POSIX.  Set REPLACE_INET_NTOP in order to avoid
+    dnl a name conflict at the linker level, even though the header file
+    dnl <ws2tcpip.h> declares inet_ntop only if _WIN32_WINNT >= 0x0600.
+    REPLACE_INET_NTOP=1
     AC_CHECK_DECLS([inet_ntop],,, [[#include <ws2tcpip.h>]])
     if test $ac_cv_have_decl_inet_ntop = yes; then
-      dnl It needs to be overridden, because the stdcall calling convention
-      dnl is not compliant with POSIX.
-      REPLACE_INET_NTOP=1
       INET_NTOP_LIB="-lws2_32"
     else
       HAVE_DECL_INET_NTOP=0
-      HAVE_INET_NTOP=0
     fi
   else
     gl_save_LIBS=$LIBS
diff --git a/m4/inet_pton.m4 b/m4/inet_pton.m4
index 72a9bc2..264892c 100644
--- a/m4/inet_pton.m4
+++ b/m4/inet_pton.m4
@@ -1,4 +1,4 @@
-# inet_pton.m4 serial 18
+# inet_pton.m4 serial 19
 dnl Copyright (C) 2006, 2008-2019 Free Software Foundation, Inc.
 dnl This file is free software; the Free Software Foundation
 dnl gives unlimited permission to copy and/or distribute it,
@@ -24,15 +24,16 @@ AC_DEFUN([gl_FUNC_INET_PTON],
   INET_PTON_LIB=
   gl_PREREQ_SYS_H_WINSOCK2
   if test $HAVE_WINSOCK2_H = 1; then
+    dnl It needs to be overridden, because the stdcall calling convention
+    dnl is not compliant with POSIX.  Set REPLACE_INET_PTON in order to avoid
+    dnl a name conflict at the linker level, even though the header file
+    dnl <ws2tcpip.h> declares inet_pton only if _WIN32_WINNT >= 0x0600.
+    REPLACE_INET_PTON=1
     AC_CHECK_DECLS([inet_pton],,, [[#include <ws2tcpip.h>]])
     if test $ac_cv_have_decl_inet_pton = yes; then
-      dnl It needs to be overridden, because the stdcall calling convention
-      dnl is not compliant with POSIX.
-      REPLACE_INET_PTON=1
       INET_PTON_LIB="-lws2_32"
     else
       HAVE_DECL_INET_PTON=0
-      HAVE_INET_PTON=0
     fi
   else
     gl_save_LIBS=$LIBS