io.c: ignore EPERM

* io.c (nogvl_copy_file_range): ignore EPERM and fallback to
  sendfile(2) or read/write. copy_file_range(2) may not exist
  even if __NR_copy_file_range is defined in the build environment.
  [Bug #14207]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@61412 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

io.c

@@ -10783,6 +10783,8 @@ nogvl_copy_file_range(struct copy_stream_struct *stp)
 	}
         switch (errno) {
 	  case EINVAL:
+	  case EPERM: /* copy_file_range(2) doesn't exist (may happen in
+			 docker container) */
 #ifdef ENOSYS
 	  case ENOSYS:
 #endif