build: use appropriate CMake variable

Author: e-kwsm

CMakeLists.txt

@@ -117,7 +117,8 @@ include_directories(${PROJECT_BINARY_DIR})
 # Compiler flags
 
 if(NOT MSVC)
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++17 -fPIC")
+  set(CMAKE_CXX_STANDARD 17)
+  set(CMAKE_POSITION_INDEPENDENT_CODE ON)
 endif()
 
 # Recurse into main project directory