KWSys 2021-06-28 (0648cb1a)

Code extracted from:

    https://gitlab.kitware.com/utils/kwsys.git

at commit 0648cb1ac5c91430b190f32319c528345b280dc3 (master).

Upstream Shortlog
-----------------

Ben Boeckel (2):
      df91e5f1 EncodingC: use NULL for pointers
      ab959cd2 SystemInformation: fix typo in comment

Björn Esser (2):
      b4a2a03c testDynamicLoader: Use LIBDL_SO macro if defined.
      b954dd54 testDynamicLoader: Use LIBC_SO if LIBDL_SO is not defined by glibc anymore.