add HHI files for new HSL _Private\_OS primitives
Summary:
This should only be called from the HSL, but we want to be able to make
2049/4107 unfixmeable, so we shouldn't add more calls to stuff without an HHI.
Longer-term, we should either:
- add an attribute similar to __Deprecated but without runtime logging - `__ImplementationDetail`, `__HSLOnly` or similar
- support package/environment boundary restrictions more generally
Reviewed By: jjergus
Differential Revision:
D20495306
fbshipit-source-id:
7b296353bf06885a9f8c4b1ea65d6651100618b4