subrepo and update asm-differ (#1664)

* git subrepo clone git@github.com:simonlindholm/asm-differ.git tools/asm-differ

subrepo:
  subdir:   "tools/asm-differ"
  merged:   "11eee5916"
upstream:
  origin:   "git@github.com:simonlindholm/asm-differ.git"
  branch:   "main"
  commit:   "11eee5916"
git-subrepo:
  version:  "0.4.6"
  origin:   "https://github.com/ingydotnet/git-subrepo"
  commit:   "110b9eb"

* ln -s ./tools/asm-differ/diff.py diff.py

tools/asm-differ/.github/workflows/unit-tests.yml

@@ -0,0 +1,15 @@
+name: unit tests
+
+on:
+  pull_request:
+  push:
+
+permissions: read-all
+
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - run: python3 -m pip install --user colorama watchdog levenshtein cxxfilt
+      - run: python3 test.py