add find belle-sip in dependency and include dirs and libs

CMakeLists.txt

@@ -193,9 +193,11 @@ endif()
 
 if(ENABLE_CONFERENCE)
 	if(LINPHONE_BUILDER_GROUP_EXTERNAL_SOURCE_PATH_BUILDERS)
+		include("${EP_bellesip_CONFIG_DIR}/BelleSIPConfig.cmake")
 		include("${EP_linphone_CONFIG_DIR}/LinphoneConfig.cmake")
 		include("${EP_linphone_CONFIG_DIR}/wrappers/cpp/LinphoneCxxConfig.cmake")
 	else ()
+		find_package(BelleSIP 1.2.4 REQUIRED)
 		find_package(Linphone REQUIRED)
 		find_package(LinphoneCxx REQUIRED)
 	endif()

src/CMakeLists.txt

@@ -194,6 +194,8 @@ if(ENABLE_PRESENCE)
 endif()
 
 if(ENABLE_CONFERENCE)
+	list(APPEND FLEXISIP_LIBS ${BELLESIP_LIBRARIES} ${LINPHONE_LIBRARIES})
+	list(APPEND FLEXISIP_INCLUDES ${BELLESIP_INCLUDE_DIRS} ${LINPHONE_INCLUDE_DIRS})
 	list(APPEND FLEXISIP_SOURCES
 		conference/conference-server.cc
 		conference/conference-server.hh