Fix assert definition

include/bits/assert.h

@@ -1,5 +1,7 @@
-#ifndef _BITS_ASSERT_H
-#define _BITS_ASSERT_H
+// Do not use include guard, to ensure assert is always defined
+#ifdef assert
+#undef assert
+#endif
 
 #ifdef NDEBUG
 # define assert(cond) (void) 0
@@ -7,5 +9,3 @@
 # define assert(cond) \
   ((void)((cond) || (__assert_fail(__func__, __FILE__, __LINE__, #cond), 0)))
 #endif
-
-#endif