Add automatic SBOM check

Author: zooba

windows-release/stage-layout-embed.yml

@@ -65,6 +65,14 @@ jobs:
       git -C "$(Pipeline.Workspace)\release-tools" checkout $(Build.SourceVersion)
     displayName: 'Clone the python/release-tools repository'
 
+  - powershell: |
+      if (-not (Test-Path "$(Build.SourcesDirectory)\Misc\externals.spdx.json")) {
+        "externals.spdx.json is missing - skipping SBOM"
+        Write-Host "##vso[task.setvariable variable=SkipSBOM]1"
+      }
+    condition: and(succeeded(), not(variables['SkipSBOM']))
+    displayName: 'Checking for SBOM'
+
   - powershell: >
       & "$(Python)"
       "$(Pipeline.Workspace)\release-tools\sbom.py"