[llvm] [CI] Upstream premerge terraform configuration (PR #117397)

[Aiden Grossman via llvm-commits]

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+# Premerge Infrastructure
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+This folder contains the terraform configuration files that define the GCP
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boomanaiden154 wrote:

We can rename it to something like `.ci/terraform`. Nesting it into something like `.ci/infrastructure/terraform` seems a bit premature to me. I don't think there are other major infrastructure pieces that we need.

Good point on bringing up Zorg. I think it makes more sense to keep all of the precommit configurations in the monorepo. The infra is somewhat coupled to the workflows/associated scripting, which have to be in the monorepo. Given that, I think keeping the infra definitions here makes sense too.

https://github.com/llvm/llvm-project/pull/117397