All files on /mnt/drive_letter are marked as executable

- All files in Windows accessed from Linux subsystem are marked with 'x' bit.
- Files such as .txt are not executable.
- Actual results (with terminal output if applicable)

```
$ ll /mnt/c/Windows/*.txt
-r-xr-xr-x 1 root root 0 Mar 15 07:49 /mnt/c/Windows/authtest.txt*
```
- Your Windows build number

14393.51
