Don't warn when using conda compilers with utils.cpp_extension (#23396)
Summary:
The conda compiler are gcc/c++ 7.3.0, but have custom version strings
for clarity:
x86_64-conda_cos6-linux-gnu-cc
x86_64-conda_cos6-linux-gnu-c++
Using these compilers to build a C++ or CUDA extension now gives this warning (unnecessarily):
```
!! WARNING !!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Your compiler (/home/rgommers/anaconda3/envs/pytorch-nightly/bin/x86_64-conda_cos6-linux-gnu-c++) is not compatible with the compiler Pytorch was
built with for this platform, which is g++ on linux.
...
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23396
Differential Revision: D16500637
Pulled By: soumith
fbshipit-source-id: 5b2fc3593e22e9a7d07dc2c0456dbb4934ffddb2
