The Watcom WMake tool has trouble running commands in paths that have
parentheses.  We already convert most commands to a shortpath for Watcom
if the path contains a space, but the use of $(CMAKE_COMMAND) hides the
true path from that conversion.  Factor the shortpath conversion code
out into a new ConvertShellCommand method.  Teach it to convert paths
that contain parentheses as well as spaces.  Use the new method to
convert the value of $(CMAKE_COMMAND) and other helper variables.