vtest: add missing includes

This fixes build failures with musl C library

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

vtest/util.c

@@ -27,6 +27,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <unistd.h>
+#include <sys/select.h>
 
 
 int vtest_wait_for_fd_read(int fd)

vtest/vtest_server.c

@@ -32,6 +32,7 @@
 #include <sys/un.h>
 #include <fcntl.h>
 #include <getopt.h>
+#include <string.h>
 
 #include "util.h"
 #include "util/u_memory.h"