[inductor] More correct check for fbcode environment (#90312)
Summary:
importing torch.fb seemed like a good idea, but we don't always have
torch.fb inside fbcode. Testing for torch.version.git_version is more
reliable, since we'll never have a git_version inside fbcode, which is an hg
repo.
Test Plan: `buck2 run mode/dev-nosan //caffe2/test/inductor:smoke`
Reviewed By: soumith, jansel
Differential Revision: D41777058
Pull Request resolved: https://github.com/pytorch/pytorch/pull/90312
Approved by: https://github.com/soumith
