atime may not updated unless strictatime is set on macOS Catalina

	Cited from mount(8):

	```
	strictatime
	        Always update the file access time when reading from a
	        file. Without this option the filesystem may default to a
	        less strict update mode, where some access time updates
	        are skipped for performance reasons. This option could be
	        ignored if it is not supported by the filesystem.
	```

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_5@67827 b2dd03c8-39d4-4d8f-98ff-823fe69b080e