[llvm] [Github] Add initial version of precommit checks (PR #80951)

[Tom Stellard via llvm-commits]

================
@@ -0,0 +1,47 @@
+name: "Precommit tests"
+
+permissions:
+  contents: read
+
+on:
+  pull_request:
+    branches:
+      - main
+    paths:
+      - '.github/workflows/precommit.yaml'
+      - 'llvm/**'
+
+jobs:
+  build-llvm:
----------------
tstellar wrote:

The job name should also be something like `build-llvm-linux` if we are planning a separate job for Windows.  The job name is the key that's used when turning on required status checks, so it should be different from the job name used for Windows.

https://github.com/llvm/llvm-project/pull/80951