Add internal facility for dynamic array handling

This is intended as a type-safe alternative to obstacks and
hand-written realloc constructs.  The implementation avoids
writing function pointers to the heap.

malloc/Versions

@@ -76,7 +76,15 @@ libc {
     __libc_scratch_buffer_grow_preserve;
     __libc_scratch_buffer_set_array_size;
 
+
     # Internal name for reallocarray
     __libc_reallocarray;
+
+    # dynarray support
+    __libc_dynarray_at_failure;
+    __libc_dynarray_emplace_enlarge;
+    __libc_dynarray_finalize;
+    __libc_dynarray_resize;
+    __libc_dynarray_resize_clear;
   }
 }