[scudo] Use MemMap in BufferPool and RegionPageMap

[fabio-d]

No description provided.

[ChiaHungDuan]

Can you separate this into 2 CLs? The first one fixes the use of static buffer as,
in RegionPageMap,

  static const uptr StaticBufferSize = 512U * sizeof(uptr);
  static BufferPool<StaticBufferCount, StaticBufferSize> Buffers;

and in the BufferPool,

static constexpr uptr NumBufferElements = (StaticBufferSize + sizeof(uptr)) / sizeof(uptr);
uptr RawBuffer[StaticBufferCount * NumBufferElements] GUARDED_BY(Mutex);

I would like to keep the BufferSize as the number of bytes.

[ChiaHungDuan]

Per discussion, we will use the number of elements and assign the type of buffer

[fabio-d]

Thanks! I've split the CL in two parts and uploaded the first part, with the changes we discussed, as #66896

Let's put this CL on hold for now until we land the new one :)