Avoid MSVC _cvtsh_ss() workaround with clang-cl (#29726)
Summary:
We (me fnabulsi bmcdb) have a handful of fixes used locally to build and run with clang-cl. I am aware of https://github.com/pytorch/pytorch/issues/8784 but it has not been touched in almost a year.
It may be more practical to upstream the non-controversial fixes piecewise. For example, this one.
Here, the dummy version of `_cvtsh_ss` for MSVC is not required (and hence causes conflicts) when using clang-cl so can be #ifdef'd out.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/29726
Differential Revision: D18478120
Pulled By: ezyang
fbshipit-source-id: cdcd94251e68347446f2ad1ac5a0e71089f7d0ab
