add mi_arena_min_alignment

include/mimalloc.h

@@ -278,6 +278,7 @@ mi_decl_export bool  mi_manage_os_memory(void* start, size_t size, bool is_commi
 
 mi_decl_export void   mi_debug_show_arenas(void) mi_attr_noexcept;
 mi_decl_export void   mi_arenas_print(void) mi_attr_noexcept;
+mi_decl_export size_t mi_arena_min_alignment(void);
 
 // Advanced: heaps associated with specific memory arena's
 typedef void* mi_arena_id_t;

src/arena.c

@@ -103,6 +103,10 @@ static bool mi_arena_has_page(mi_arena_t* arena, mi_page_t* page) {
 }
 #endif
 
+size_t mi_arena_min_alignment() {
+  return MI_ARENA_SLICE_ALIGN;
+}
+
 /* -----------------------------------------------------------
   Util
 ----------------------------------------------------------- */