include sys/select.h to prevent picky compiler warnings when using select()

without proto

tests/libtest/lib503.c

@@ -5,6 +5,9 @@
 #endif
 #include <sys/time.h>
 #include <sys/types.h>
+#ifdef HAVE_SYS_SELECT_H
+#include <sys/select.h>
+#endif
 
 /*
  * Source code in here hugely as reported in bug report 651460 by

tests/libtest/lib504.c

@@ -5,6 +5,9 @@
 #endif
 #include <sys/time.h>
 #include <sys/types.h>
+#ifdef HAVE_SYS_SELECT_H
+#include <sys/select.h>
+#endif
 
 /*
  * Source code in here hugely as reported in bug report 651464 by

tests/libtest/lib507.c

 #include "test.h"
 
+#ifdef HAVE_SYS_SOCKET_H
+#include <sys/socket.h>
+#endif
+#ifdef HAVE_SYS_SELECT_H
+#include <sys/select.h>
+#endif
+
 int test(char *URL)
 {
   CURL* curls;

tests/libtest/lib509.c

@@ -7,6 +7,9 @@
 #endif
 #include <sys/time.h>
 #include <sys/types.h>
+#ifdef HAVE_SYS_SELECT_H
+#include <sys/select.h>
+#endif
 
 #include <openssl/opensslv.h>
 #include <openssl/x509v3.h>