fix cmake c-standard perporty

hanke0 · hanke0 · commit 36652eb4e8b8 · 2020-06-28T19:45:35.000+08:00
diff --git a/CMakeLists.txt b/CMakeLists.txt
@@ -1,7 +1,8 @@
 cmake_minimum_required(VERSION 3.12)
 project(python_ctools C)
 
-set(CMAKE_C_STANDARD C99)
+set(CMAKE_C_STANDARD 99)
+set(C_STANDARD_REQUIRED ON)
 
 set(CMAKE_LIBRARY_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/lib)
 
