InnoDB hash_table_t::array is not aligned to cache line size

After MDEV-35190 and some other recent changes, there is some further room for improvement in the InnoDB hash table implementation.

If we aligned the hash_table_t::array to CPU_LEVEL1_DCACHE_LINESIZE, there could be some benefit for smaller hash tables. On IA-32 and x86-64 we assume that the cache line size is 64 bytes. On ARMv8 and POWER it is assumed to be 128 bytes, and on s390x it is 256 bytes. That would correspond to 8 to 32 pointers per cache line, or 16 pointers on the IA-32.