[PATCH] Fix INET6 detection on recent clang

[Chris Webb]

The implicit int return for main() in the configure test for INET6 is
now a hard error on recent clang, breaking the detection of IPv6 support.
Update this to int main(void) like the other configure tests.

The problem this causes in practice is quite subtle and easy to miss.
ssh is always run with -4 which works fine except when there is only v6
connectivity between a pair of hosts, whereupon ssh between them works
but rsync unexpectedly fails with 'Name has no usable address'.

Signed-off-by: Chris Webb <chris at arachsys.com>
---
 configure.ac | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/configure.ac b/configure.ac
index ccad7f13..9a766c94 100644
--- a/configure.ac
+++ b/configure.ac
@@ -392,7 +392,7 @@ AS_HELP_STRING([--disable-ipv6],[disable to omit ipv6 support]),
 #include <stdlib.h>
 #include <sys/types.h>
 #include <sys/socket.h>
-main()
+int main(void)
 {
    if (socket(AF_INET6, SOCK_STREAM, 0) < 0)
      exit(1);