LIBXSMM package: add version 1.13 and optional shared libs (#11998)
LIBXSMM package: add version 1.13 and optional shared libs (#11998)

* Add +shared variant, which builds shared library in addition to the
  static library.
* Install libraries even when specifying the header-only option
  (header-only is just about installing an additional folder).
* An additional make call is not required to build generator
  executables (they are built by default).
* Streamlined help-line of each variant.
iulian787/spack,LLNL/spack,LLNL/spack,iulian787/spack,LLNL/spack,iulian787/spack,LLNL/spack,iulian787/spack,LLNL/spack,iulian787/spack