[contrib/pzstd] Detect and Select Maximum Available C++ Standard

[contrib/pzstd] Detect and Select Maximum Available C++ Standard

Rather than remove the flag entirely, as proposed in #3499, this commit uses
the newest C++ standard the compiler supports. This retains the selection of
using only standardized features (excluding GNU extensions) and keeps the
recency requirements of the codebase explicit.

Tested with various versions of `g++` and `clang++`.