I was investigating the CI failures for JavaScript, and found another issue, testing on macOS. In `h$base_fillStat` in `jsbits/base.js`, we fill the `fs_mode` field with the file mode from nodejs, which comes from the host platform. Accessors that use JavaScript to test for file types work correctly, since we use `h$fs.constants` to test the file type bits, which match the ones from the host platform. But some Haskell code accesses the mode bits directly, using an `.hsc` file: `System/Posix/Files/Common.hsc`, and that gives the wrong filetypes on macOS. Fix: we should convert the mode field before inserting it in the struct stat to match the values that the C compiler accepts.