Fix undefined symbol errors when building for wasi #758, by @anuraaga

include/mimalloc/internal.h

@@ -296,6 +296,12 @@ static inline uintptr_t _mi_align_up(uintptr_t sz, size_t alignment) {
   }
 }
 
+// Align a pointer upwards
+static inline void* mi_align_up_ptr(void* p, size_t alignment) {
+  return (void*)_mi_align_up((uintptr_t)p, alignment);
+}
+
+
 // Divide upwards: `s <= _mi_divide_up(s,d)*d < s+d`.
 static inline uintptr_t _mi_divide_up(uintptr_t size, size_t divider) {
   mi_assert_internal(divider != 0);