https://bugs.gentoo.org/951839
https://github.com/Tencent/rapidjson/issues/2159 fixed in git already

--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,4 +1,4 @@
-CMAKE_MINIMUM_REQUIRED(VERSION 2.8)
+CMAKE_MINIMUM_REQUIRED(VERSION 3.5)
 if(POLICY CMP0025)
   # detect Apple's Clang
   cmake_policy(SET CMP0025 NEW)
--- a/example/CMakeLists.txt
+++ b/example/CMakeLists.txt
@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8)
+cmake_minimum_required(VERSION 3.5)
 
 if(POLICY CMP0054)
   cmake_policy(SET CMP0054 NEW)