[pytorch] Fix MSVC unexpected tokens following preprocessor directive (#105922)
Summary:
Fix this warning:
```
caffe2\c10\macros\Macros.h(138): warning C4067: unexpected tokens following preprocessor directive - expected a newline
```
`caffe2/c10/util/variant.h` already has a similar to check and define a stub for `__has_attribute(x)`, so this would not be new to caffe2/pytorch.
Test Plan: CI should complete, still with plenty of caffe2 warnings but this one should be gone from the Windows build log
Differential Revision: D47735319
Pull Request resolved: https://github.com/pytorch/pytorch/pull/105922
Approved by: https://github.com/kit1980
