* ext/openssl/depend: remove dependency from internal headers.
  [Feature #9612]
* ext/openssl/ossl.c (ossl_fips_mode_set): ditto.
* ext/coverage/depend: ditto.
* include/ruby/thread_native.h: added.
  This header file only provides wrapper functions to control
  native threads. These wrapper functions are used by MRI
  implementation.
* vm_core.h: use include/ruby/thread_native.h.
* thread.c: ditto.
* thread_pthread.h: ditto.
* thread_win32.h: ditto.
* thread_native.h: removed.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@45944 b2dd03c8-39d4-4d8f-98ff-823fe69b080e