- give precedence to ~openmp (-no-openmp) over +openmp (-openmp)
  in the general rules and in the Makefile. This makes it robuster
  when specifying +openmp in general, but ~openmp for specific build
  components.

- disable openmp for OSspecific and Pstream components.
  Neither should contain any openmp code anyhow.

  Additionally, since OSspecific is generally built as a static
  object, it can become problematic (eg, with AMD ROCm) if the
  compiler generates information that openmp is required but then uses
  static linkage.