KWSys 2019-01-24 (b9dd1636)

Code extracted from:

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

at commit b9dd1636e50ea43cd33bed8c6ffbbe7161618b54 (master).

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

Ben Boeckel (1):
      28db6989 cmake: add an option for building with PIC

Taylor Braun-Jones (1):
      3f35954d SystemTools: Add TextFilesDiffer method

Tobias Kloss (1):
      aa1f7f7c SystemTools: Fix FileIsSymlink with Windows data deduplication