ConfigureChecks: Add support for system not expecting "libutil" (e.g VxWorks)
ConfigureChecks: Add support for system not expecting "libutil" (e.g VxWorks)

See #163

adrianbroher/python-cmake-buildsystem,python-cmake-buildsystem/python-cmake-buildsystem,thewtex/python-cmake-buildsystem,thewtex/python-cmake-buildsystem,davidsansome/python-cmake-buildsystem