[ruby/prism] Fix windows build checking for _POSIX_MAPPED_FILES
https://github.com/ruby/prism/commit/acf603603f
[ruby/prism] Fix windows build checking for _POSIX_MAPPED_FILES
https://github.com/ruby/prism/commit/acf603603f