add -fvisibility=hidden to CMake

Author: q4a

CMakeLists.txt

@@ -65,7 +65,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU")
     endif()
 endif()
 
-set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive --std=c++17 -Wno-attributes -pipe")
+set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive --std=c++17 -Wno-attributes -pipe -fvisibility=hidden")
 #set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fpermissive") This is for the future versions
 #set(CMAKE_CXX_STANDARD 14) #Otherwise adds -std=gnu++11 and breaks successful building
 #set(CMAKE_CXX_STANDARD_REQUIRED ON)