Fix export macros (#15856)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/15856
They seem to be wrong.
cc zdevito to take a look but I think this is now more correct.
It's weird this didn't cause linker errors. Probably, this functionality isn't used across library boundaries yet.
Reviewed By: dzhulgakov
Differential Revision: D13605257
fbshipit-source-id: 7077ca9027c3ac79a4847ec15ead7ddb28696445
