https://sources.debian.org/patches/linphone-desktop/4.2.5-3/0001-do-not-build-linphone-sdk.patch/

Index: linphone-app/cmake_builder/additional_steps.cmake
--- linphone-app/cmake_builder/additional_steps.cmake.orig
+++ linphone-app/cmake_builder/additional_steps.cmake
@@ -54,14 +54,5 @@ if (ENABLE_PACKAGING)
     linphone_builder_apply_flags()
     linphone_builder_set_ep_directories(linphone_package)
     linphone_builder_expand_external_project_vars()
-    ExternalProject_Add(TARGET_linphone_package
-      DEPENDS TARGET_linphone_builder
-      TMP_DIR ${ep_tmp}
-      BINARY_DIR ${ep_build}
-      SOURCE_DIR "${CMAKE_CURRENT_LIST_DIR}/linphone_package"
-      DOWNLOAD_COMMAND ""
-      CMAKE_GENERATOR ${CMAKE_GENERATOR}
-      CMAKE_ARGS ${LINPHONE_BUILDER_EP_ARGS} -DCMAKE_INSTALL_PREFIX=${LINPHONE_BUILDER_WORK_DIR}/PACKAGE -DTOOLS_DIR=${CMAKE_BINARY_DIR}/programs -DLINPHONE_OUTPUT_DIR=${CMAKE_INSTALL_PREFIX} -DLINPHONE_DESKTOP_DIR=${CMAKE_CURRENT_LIST_DIR}/.. -DLINPHONE_SOURCE_DIR=${EP_linphone_SOURCE_DIR} ${ENABLE_VARIABLES} -DLINPHONE_BUILDER_SIGNING_IDENTITY=${LINPHONE_BUILDER_SIGNING_IDENTITY}
-    )
   endif ()
 endif ()
