Fix cmake warning (#42707)
Summary:
If argumenets in set_target_properties are not separated by whitespace, cmake raises a warning:
```
CMake Warning (dev) at cmake/public/cuda.cmake:269:
Syntax Warning in cmake code at column 54
Argument not separated from preceding token by whitespace.
```
Fixes #{issue number}
Pull Request resolved: https://github.com/pytorch/pytorch/pull/42707
Reviewed By: ailzhang
Differential Revision: D22988055
Pulled By: malfet
fbshipit-source-id: c3744f23b383d603788cd36f89a8286a46b6c00f
