Details:
- Defined dummy versions of bli_l3_sup_thread_decorator() for Openmp
and pthreads so that those builds don't fail when performing shared
library linking (especially for Windows DLLs via AppVeyor). For now,
these dummy implementations of bli_l3_sup_thread_decorator() are
merely carbon-copies of the implementation provided for single-
threaded execution (ie: the one found in bli_l3_sup_decor_single.c).
Thus, an OpenMP or pthreads build will be able to use the gemmsup
code (including the new selective packing functionality), as it did
before 39fa7136, even though it will not actually employ any
multithreaded parallelism.