[ROCm] allow PYTORCH_ROCM_ARCH in cpp_extension.py (#54341)
Summary:
Allows extensions to override ROCm gfx arch targets. Reuses the same env var used during cmake build for consistency.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/54341
Reviewed By: bdhirsh
Differential Revision: D27244010
Pulled By: heitorschueroff
fbshipit-source-id: 279e1a41ee395a0596aa7f696b6e908cf7f5bb83
