CI: install llvm-strip and verify bpf2go output is in sync

bpf2go shells out to llvm-strip to drop DWARF from the embedded .o;
ubuntu-latest has clang but not llvm-strip on PATH. Install the llvm
package alongside libbpf-dev / linux-libc-dev.

Also add a git diff --exit-code guard after make probes-bpf so PRs
that edit probe.bpf.c without committing the regenerated probe_bpfel.go
fail Test instead of merging out of sync.

Author: gnurizen

.github/workflows/test.yml

@@ -24,14 +24,21 @@ jobs:
       # `probes/probe_bpfel.go` (bpf2go-generated) has `//go:embed
       # probe_bpfel.o`, so the package fails to compile without the .o on
       # disk. Regenerate it before tests; clang ships on ubuntu-latest, we
-      # just need the libbpf + kernel UAPI headers.
+      # need libbpf + kernel UAPI headers, plus `llvm` for the `llvm-strip`
+      # that bpf2go runs to strip DWARF from the embedded .o.
       - name: Install BPF build dependencies
         run: |
           sudo apt-get update
-          sudo apt-get install -y --no-install-recommends libbpf-dev linux-libc-dev
+          sudo apt-get install -y --no-install-recommends libbpf-dev linux-libc-dev llvm
 
       - name: Generate probes BPF object
         run: make probes-bpf
 
+      # Catch "edited probe.bpf.c but forgot to regenerate / commit
+      # probe_bpfel.go" before merge — bpf2go output is deterministic, so
+      # any drift surfaces here.
+      - name: Verify generated bpf2go output is in sync
+        run: git diff --exit-code probes/probe_bpfel.go
+
       - name: Run Tests
         run: go test -race -v ./...