cmake : update to 3.19 (#351)

- update from 3.0 (from 2014) to 3.19 (from 2020)
- move some global setting onto the targets (through a cmake include)

examples/command/CMakeLists.txt

@@ -2,6 +2,9 @@ if (WHISPER_SUPPORT_SDL2)
     # command
     set(TARGET command)
     add_executable(${TARGET} command.cpp)
+
+    include(DefaultTargetOptions)
+
     target_include_directories(${TARGET} PRIVATE ${SDL2_INCLUDE_DIRS})
     target_link_libraries(${TARGET} PRIVATE whisper ${SDL2_LIBRARIES} ${CMAKE_THREAD_LIBS_INIT})
 endif ()