Suppress `warning: calling a constexpr __host__ function from a __host__ __device__ function is not allowed` warning (#49197)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49197
Compiling currently gives a number of these warnings:
```
caffe2/c10/util/TypeCast.h(27): warning: calling a constexpr __host__ function from a __host__ __device__ function is not allowed. The experimental flag '--expt-relaxed-constexpr' can be used to allow this.
detected during:
instantiation of "decltype(auto) c10::maybe_real<true, src_t>::apply(src_t) [with src_t=c10::complex<double>]"
(57): here
instantiation of "uint8_t c10::static_cast_with_inter_type<uint8_t, src_t>::apply(src_t) [with src_t=c10::complex<double>]"
(157): here
instantiation of "To c10::convert<To,From>(From) [with To=uint8_t, From=c10::complex<double>]"
(169): here
instantiation of "To c10::checked_convert<To,From>(From, const char *) [with To=uint8_t, From=c10::complex<double>]"
caffe2/c10/co
```
Here we fix this by adding `C10_HOST_DEVICE` to the offending function.
Test Plan:
Compiling
```
buck build mode/dev-nosan -c=python.package_style=inplace dper3/dper3_models/experimental/pytorch/ads:ads_model_generation_script
```
shows this warning.
We rely on sandcastle for testing here.
Reviewed By: xw285cornell
Differential Revision: D25440771
fbshipit-source-id: 876c412eb06e8837978061cc4793abda42fac821
