[AIX] Implement AIX special bitfield related alignment rules

1.[bool, char, short] bitfields have the same alignment as unsigned int
2.Adjust alignment on typedef field decls/honor align attribute
3.Fix alignment for scoped enum class
4.Long long bitfield has 4bytes alignment and StorageUnitSize under 32 bit
  compile mode

Differential Revision: https://reviews.llvm.org/D87029