Boost.Math multiprc_concept_check_6 failing with Clang-14 and C++17

[mborland]

Under Clang-14 with C++17 there is a new error here: https://github.com/boostorg/math/actions/runs/4447933117/jobs/7810075798#step:17:1835 saying that number base is an incomplete type. It doesn't look like any other version of clang is effected https://drone.cpp.al/boostorg/math/1267.

[jzmaddock]

The code that caused this has been reverted, should be fixed now.