github/workflows: Add sanitize_undefined workflow to unix port CI.

gcc's "undefined behavior" sanitizer can catch a range of misbehaviors at
runtime that normally go unnoticed.  These include integer and pointer
operations that are "undefined" per the relevant C specification.

This commit enables undefined behavior detection during a new unix
coverage-like build.

Signed-off-by: Jeff Epler <jepler@gmail.com>

.github/workflows/ports_unix.yml

@@ -262,3 +262,23 @@ jobs:
     - name: Print failures
       if: failure()
       run: tests/run-tests.py --print-failures
+
+  sanitize_undefined:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install packages
+      run: source tools/ci.sh && ci_unix_coverage_setup
+    - name: Build
+      run: source tools/ci.sh && ci_unix_sanitize_undefined_build
+    - name: Run main test suite
+      run: source tools/ci.sh && ci_unix_sanitize_undefined_run_tests
+    - name: Test merging .mpy files
+      run: source tools/ci.sh && ci_unix_coverage_run_mpy_merge_tests
+    - name: Build native mpy modules
+      run: source tools/ci.sh && ci_native_mpy_modules_build
+    - name: Test importing .mpy generated by mpy_ld.py
+      run: source tools/ci.sh && ci_unix_coverage_run_native_mpy_tests
+    - name: Print failures
+      if: failure()
+      run: tests/run-tests.py --print-failures