cmake _HAVE_FORK examples

Kitware/VTK ThirdParty/hdf5/vtkhdf5/config/cmake_ext_mod/ConfigureChecks.cmake :442 

CHECK_FUNCTION_EXISTS (fork              ${HDF_PREFIX}_HAVE_FORK)

HDFGroup/hdf5 config/ConfigureChecks.cmake :425 

CHECK_FUNCTION_EXISTS (fork              ${HDF_PREFIX}_HAVE_FORK)

InsightSoftwareConsortium/ITK Modules/ThirdParty/HDF5/src/itkhdf5/config/cmake/ConfigureChecks.cmake :409 

CHECK_FUNCTION_EXISTS (fork              ${HDF_PREFIX}_HAVE_FORK)

Tencent/Forward source/third_party/hdf5/config/cmake_ext_mod/ConfigureChecks.cmake :493 

CHECK_FUNCTION_EXISTS (fork              ${HDF_PREFIX}_HAVE_FORK)