lib: avoid include loop with assert.h

`assert.h` -> `xref.h` -> `typesafe.h` -> `assert.h`

Might be possible to do this more cleanly some way, but that way is not
obvious, so here's the "simple & dumb" approach.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>

lib/atomlist.c

@@ -18,6 +18,8 @@
 #include "config.h"
 #endif
 
+#include <assert.h>
+
 #include "atomlist.h"
 
 void atomlist_add_head(struct atomlist_head *h, struct atomlist_item *item)

lib/frrcu.h

@@ -17,6 +17,8 @@
 #ifndef _FRRCU_H
 #define _FRRCU_H
 
+#include <assert.h>
+
 #include "memory.h"
 #include "atomlist.h"
 

lib/typesafe.c

@@ -20,6 +20,7 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <assert.h>
 
 #include "typesafe.h"
 #include "memory.h"

lib/typesafe.h

@@ -20,7 +20,6 @@
 #include <stddef.h>
 #include <stdint.h>
 #include <stdbool.h>
-#include <assert.h>
 #include "compiler.h"
 
 #ifdef __cplusplus