Revert "Use compiler intrinsic instead of assembly for popcnt"

This reverts commit a69f1d7c2060dc7b320a7b4801105df00b22a96a.
Use compiler intrinsic instead of assembly for popcnt
This time, do not break compatibility with some AMD machines that have SSE3 and popcnt, but do
not have SSE4.2.

No functional change.
size_t cast in TranspositionTable::first_entry()
32-bit truncation would make this function bogus when clusterCount >= 2^33 (ie. Hash >= 256 GB).

No function change.
Merge branch 'master' into nolsb
Threats -25% to compensate (8443537)