libstdc++ possibly optimizes shared_ptr<T> when not linking pthreads

[gmbeard]

From the README...

Observations

[...]
C++ "ref-counted" (shared_ptr) has significant performance hit on non-Linux platforms.

Apparently, libstdc++ contains an optimization for shared_ptr<T> whereby it is able to fall back to a non-atomic reference count if it detects the absence of pthreads (source: http://snf.github.io/2019/02/13/shared-ptr-optimization/).

This could explain the performance disparity between different platforms. Should the C++ build(s) link to pthreads to disable this optimization?