Fix compilation error:

src/core/core.cpp:428:2: error: void function 'doLater' should not return a
value [-Wreturn-type]
--- CMakeLists.txt.orig	2023-03-17 13:29:37 UTC
+++ CMakeLists.txt
@@ -4,7 +4,7 @@
 #
 ############################################################################
 #
-# This file is part of Liblinphone 
+# This file is part of Liblinphone
 # (see https://gitlab.linphone.org/BC/public/liblinphone).
 #
 # This program is free software: you can redistribute it and/or modify
@@ -354,7 +354,7 @@ else()
 	list(APPEND STRICT_OPTIONS_CPP
 		"-Wall"
 		"-Wconversion"
-		"-Werror=return-type"
+		"-Wno-error=return-type"
 		"-Winit-self"
 		"-Wno-error=deprecated-declarations"
 		"-Wpointer-arith"