[llvm] workflows/precommit: Use single shared job to compute projects (PR #224941)

[Aiden Grossman via llvm-commits]

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@@ -23,12 +23,61 @@ concurrency:
   cancel-in-progress: true
 
 jobs:
+  # Computes which projects/check-targets to build and test on the
+  # self-hosted macOS runners.
+  premerge-compute:
+    name: Compute Projects
+    if: >-
+        github.repository_owner == 'llvm' &&
+        (github.event_name != 'pull_request' || github.event.action != 'closed')
+    runs-on: ubuntu-22.04
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boomanaiden154 wrote:

`ubuntu-24.04` to be consistent with other jobs?

https://github.com/llvm/llvm-project/pull/224941