Add missing include files and implicit ints to support building
with a compiler in strict(er) C99 mode.

diff --git a/config/config.poll-dev.c b/config/config.poll-dev.c
index 413a6a7ad307b8ed..ec323874064c8643 100644
--- a/config/config.poll-dev.c
+++ b/config/config.poll-dev.c
@@ -6,6 +6,7 @@
 #include <stdio.h>
 #include <fcntl.h>
 #include <poll.h>
+#include <unistd.h>
 
 int
 main()
diff --git a/config/config.proccmd.c b/config/config.proccmd.c
index b27d25a56d07b287..3e5a5a38792ee414 100644
--- a/config/config.proccmd.c
+++ b/config/config.proccmd.c
@@ -10,6 +10,8 @@
   notice and this notice are preserved.
 */
 #include <stdio.h>
+#include <unistd.h>
+
 int main()
 {
   char	buf[32];
diff --git a/config/config.reuseaddr.c b/config/config.reuseaddr.c
index 45276c8cdf793ba4..6061b7814ef5a457 100644
--- a/config/config.reuseaddr.c
+++ b/config/config.reuseaddr.c
@@ -31,7 +31,7 @@
 // Maximum data in single I/O operation
 #define	NETBUF_SIZE	4096
 
-main()
+int main()
 {
   struct sockaddr_in	sin;
   int	size = sizeof(sin);
diff --git a/config/config.vasprintf.c b/config/config.vasprintf.c
index a3c755ec95c34155..f532502e1d3fba95 100644
--- a/config/config.vasprintf.c
+++ b/config/config.vasprintf.c
@@ -25,6 +25,6 @@ static int func(const char *fmt, ...)
 int main()
 {
   if (func("1234", 0) == 4)
-    exit (0);
-  exit (-1);
+    return 0;
+  return -1;
 }
diff --git a/config/config.vsprintf.c b/config/config.vsprintf.c
index 01a383d6170ed9ff..a4a971e8029425bc 100644
--- a/config/config.vsprintf.c
+++ b/config/config.vsprintf.c
@@ -25,6 +25,6 @@ static int func(const char *fmt, ...)
 int main()
 {
   if (func("1234", 0) == 4)
-    exit (0);
-  exit (-1);
+    return 0;
+  return -1;
 }