it also works on file names with special characters.


Build-tools/Do-compile:
  Ever and again, some test creates a file name with special characters that need to be
  escaped when passed to the shell; as this is not done, 'system("rm -f ...");' fails
  on them, the old test tree is not deleted, and the build fails.
  Prevent this by changing to Perl 'unlink()' which does not need escaping.