cmake LWS_HAVE_VFORK examples

warmcat/libwebsockets CMakeLists.txt :650 

CHECK_FUNCTION_EXISTS(vfork LWS_HAVE_VFORK)

c-jimenez/open-ocpp 3rdparty/libwebsockets/CMakeLists.txt :574 

CHECK_FUNCTION_EXISTS(vfork LWS_HAVE_VFORK)

fluffos/fluffos src/thirdparty/libwebsockets/CMakeLists.txt :557 

CHECK_FUNCTION_EXISTS(vfork LWS_HAVE_VFORK)