[MLIR][Presburger] introduce MPInt to support fast arbitrary precision in Presburger

This uses an int64_t-based fastpath for the common case and falls back to
SlowMPInt to handle the rare cases where larger numbers occur.
It uses `__builtin_*` for performance through the support in LLVM MathExtras.

Using this in the Presburger library results in a minor performance
*improvement* over any commit hash before sequence of patches
starting at d5e31cf3.

Reviewed By: Groverkss, ftynse

Differential Revision: https://reviews.llvm.org/D128811