mingw10.dll 의존성 제거하기

옵션으로 -mthreads를 주게 되면 dependency가 발생한다.
-mthreads옵션은 __gthread_key_create가 필요한 경우에만 의미가 있다.

The gcc manual says

-mthreads
Support thread-safe exception handling on Mingw32. Code that relies on thread-safe exception handling must compile and link all code with the -mthreads option. When compiling,
-mthreads defines -D_MT; when linking, it links in a special thread helper library -lmingwthrd which cleans up per thread exception handling data.