[libcxx] Add strict weak ordering checks to sorting algorithms

This is the implementation of the first proposal of strict weak ordering checks described in https://discourse.llvm.org/t/rfc-strict-weak-ordering-checks-in-the-debug-libc/70217

This targets the most vulnerable algorithms like std::sort

Reviewed By: philnik, #libc

Differential Revision: https://reviews.llvm.org/D150264