--- ./linphone-sdk/external/libxml2/CMakeLists.txt.ori	2019-10-22 01:30:59.098615599 +0200
+++ ./linphone-sdk/external/libxml2/CMakeLists.txt	2019-10-22 01:32:01.514309732 +0200
@@ -30,7 +30,7 @@
 set(VERSION "${LIBXML_MAJOR_VERSION}.${LIBXML_MINOR_VERSION}.${LIBXML_MICRO_VERSION}")
 set(LIBXML_VERSION_NUMBER 208000)
 
-
+include(CheckSymbolExists)
 include(CMakeDependentOption)
 
 option(ENABLE_STATIC "Build static library (default is shared library)." NO)
--- ./linphone-sdk/ortp/CMakeLists.txt.ori	2019-10-22 01:30:46.890675423 +0200
+++ ./linphone-sdk/ortp/CMakeLists.txt	2019-10-22 01:32:08.379276091 +0200
@@ -42,6 +42,7 @@
 set(WITH_THREAD_STACK_SIZE "0" CACHE STRING "Set thread stack size (0 is the OS default).")
 
 
+include(CheckSymbolExists)
 include(CheckIncludeFile)
 include(CheckFunctionExists)
 include(GNUInstallDirs)
--- ./linphone-sdk/bctoolbox/CMakeLists.txt.ori	2019-10-22 01:30:29.945758462 +0200
+++ ./linphone-sdk/bctoolbox/CMakeLists.txt	2019-10-22 01:32:14.095248080 +0200
@@ -49,6 +49,7 @@
 option(ENABLE_TESTS "Enable compilation of tests" ON)
 
 
+include(CheckSymbolExists)
 include(CheckLibraryExists)
 include(CheckSymbolExists)
 include(CheckCSourceCompiles)
--- ./linphone-sdk/belle-sip/CMakeLists.txt.ori	2019-10-22 01:30:21.537799665 +0200
+++ ./linphone-sdk/belle-sip/CMakeLists.txt	2019-10-22 01:32:22.250208117 +0200
@@ -43,6 +43,7 @@
 option(ENABLE_MDNS "Enable multicast DNS" OFF)
 
 
+include(CheckSymbolExists)
 include(CheckLibraryExists)
 include(CheckSymbolExists)
 include(CheckCSourceCompiles)