Fix build when shared libraries are disabled

On some platforms, shared libraries are not used. The stub code
need some updating to not generate errors.
diff --git a/ip/static-syms.c b/ip/static-syms.c
index 1ed3a8a..0bc8074 100644
--- a/ip/static-syms.c
+++ b/ip/static-syms.c
@@ -1,4 +1,12 @@
+/*
+ * This file creates a dummy version of dynamic loading
+ * for environments where dynamic linking
+ * is not used or available.
+ */
+
 #include <string.h>
+#include "dlfcn.h"
+
 void *_dlsym(const char *sym)
 {
 #include "static-syms.h"