List supported build types in top-level CMakeLists.txt

CMakeLists.txt

@@ -1,5 +1,7 @@
 cmake_minimum_required(VERSION 3.10)
 
+set (CMAKE_CONFIGURATION_TYPES "Debug;Release")
+
 project(lwIP)
 
 # Example lwIP application

contrib/ports/unix/check/CMakeLists.txt

@@ -1,5 +1,7 @@
 cmake_minimum_required(VERSION 3.8)
 
+set (CMAKE_CONFIGURATION_TYPES "Debug;Release")
+
 project(lwipunittests C)
 
 if (NOT CMAKE_SYSTEM_NAME STREQUAL "Linux" AND NOT CMAKE_SYSTEM_NAME STREQUAL "Darwin")