CMake/Help/release/dev/WCDH-thread_local.rst

WriteCompilerDetectionHeader thread_local portability
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* The :module:`WriteCompilerDetectionHeader` module learned to
  create a define for portability of the cxx_thread_local feature. The define
  expands to either the C++11 ``thread_local`` keyword, or a
  pre-standardization compiler-specific equivalent, as appropriate.