message: mini_heap: rejigger spanStart type
diff: @@ -374,7 +374,7 @@ public:
  }
  inline ssize_t ATTRIBUTE_ALWAYS_INLINE getOff(void *arenaBegin, void *ptr) const {
  - const auto span = spanStart(arenaBegin, ptr);
  + const auto span = spanStart(reinterpret_cast<uintptr_t>(arenaBegin), ptr);
  d_assert(span != 0);
  const auto ptrval = reinterpret_cast<uintptr_t>(ptr);
  @@ -390,14 +390,13 @@ public:
  }
  protected:
  - inline uintptr_t ATTRIBUTE_ALWAYS_INLINE spanStart(void *arenaBegin, void *ptr) const {
  - const auto arena = reinterpret_cast<uintptr_t>(arenaBegin);
  + inline uintptr_t ATTRIBUTE_ALWAYS_INLINE spanStart(uintptr_t arenaBegin, void *ptr) const {
  const auto ptrval = reinterpret_cast<uintptr_t>(ptr);
  const auto len = _span.byteLength();
  // manually unroll loop once to capture the common case of
  // un-meshed miniheaps
  - uintptr_t spanptr = arena + _span.offset * kPageSize;
  + uintptr_t spanptr = arenaBegin + _span.offset * kPageSize;
  if (likely(spanptr <= ptrval && ptrval < spanptr + len))
  return spanptr;
  @@ -408,7 +407,7 @@ protected:
  }
  GetMiniHeap(_nextMiniHeap)->forEachMeshed([&](const MiniHeap *mh) {
  - uintptr_t meshedSpanptr = arena + mh->span().offset * kPageSize;
  + uintptr_t meshedSpanptr = arenaBegin + mh->span().offset * kPageSize;
  if (meshedSpanptr <= ptrval && ptrval < meshedSpanptr + len) {
  spanptr = meshedSpanptr;
  return true;
  