ai_flags in calls to getaddrinfo

[Eli Zaretskii <eliz@gnu.org>]

On one of the systems on which I work, getaddrinfo called with
AF_INET6 fails with EAI_NODATA, for some reason.  That causes
network-lookup-address-info to fail when passed 'ipv6' as the last
argument.

Adding the AI_V4MAPPED flag, as in the patch below, seems to solve the
problem.  So I wonder why we don't do this in general.  I'm not an
expert on DNS, so would people who know more than I do about this
please comment on whether the patch below is a good idea?

diff --git a/src/process.c b/src/process.c
index 28ab15c903..f550703c2a 100644
--- a/src/process.c
+++ b/src/process.c
@@ -4559,12 +4559,18 @@ DEFUN ("network-lookup-address-info", Fnetwork_lookup_address_info,
 
   memset (&hints, 0, sizeof hints);
   if (EQ (family, Qnil))
-    hints.ai_family = AF_UNSPEC;
+    {
+      hints.ai_family = AF_UNSPEC;
+      hints.ai_flags = AI_ALL | AI_V4MAPPED;
+    }
   else if (EQ (family, Qipv4))
     hints.ai_family = AF_INET;
 #ifdef AF_INET6
   else if (EQ (family, Qipv6))
-    hints.ai_family = AF_INET6;
+    {
+      hints.ai_family = AF_INET6;
+      hints.ai_flags = AI_V4MAPPED;
+    }
 #endif
   else
     error ("Unsupported lookup type");