cmake HAVE_WORKING_VFORK examples

InsightSoftwareConsortium/ITK Modules/ThirdParty/MINC/src/libminc/CMakeLists.txt :132 

CHECK_FUNCTION_EXISTS(vfork    HAVE_WORKING_VFORK)

snl-dakota/dakota src/CMakeLists.txt :184 

add_definitions("-DHAVE_WORKING_VFORK")