Do not use clang if it can not parse system extensions (#34549)
Summary:
Attempt to build pytorch with ASAN on system with gcc-8 fails due to the mismatch system compilation flags.
Address the issue by using original compiler to build `torch._C` extension
Pull Request resolved: https://github.com/pytorch/pytorch/pull/34549
Test Plan: Run `.jenkins/pytorch/build-asan.sh` on FC-30
Differential Revision: D20373781
Pulled By: malfet
fbshipit-source-id: 041c8d25f96b4436385a5e0eb6fc46e9b5fdf3f1
