[CircleCI] Add Python3.8-gcc9 config (#38747)
Summary:
`pytorch-linux-bionic-py3.8-gcc9` is based on Ubuntu 18.04 using gcc-9 and python-3.8
`pytorch-linux-bionic-cuda10.2-cudnn7-py3.8-gcc9` adds CUDA-10.2 to the same configuration
Also this in this PR:
- Updates valgrind to 3.15.0
- Fixes bug when gcc-5.5 were used in gcc-5.4 configurations
- Do not install `typing` when installing Python-3.8 from Conda
- Install `llvmdev-8` to for `numba/llvmlite` package compilation to succeed
Pull Request resolved: https://github.com/pytorch/pytorch/pull/38747
Differential Revision: D21670093
Pulled By: malfet
fbshipit-source-id: 995dfc20118a6945b55a81ef665a0b80dab97535
