Update debug flag for vulkan (#85715)
DEBUG is too generic name and when building some other target it seems to
conflict with it, so defining VULKAN_DEBUG
Differential Revision: [D39449772](https://our.internmc.facebook.com/intern/diff/D39449772/)
**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D39449772/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/85715
Approved by: https://github.com/SS-JIA
