scripts: Add Cppcheck with native build contexts

Expose make cppcheck using freshly captured kernel CHECK commands and
real userspace compiler invocations. Keep their include paths and
definitions unchanged and analyze kernel and userspace contexts
separately.

Use the shared source scope without additional input exclusions, project
models or diagnostic suppressions. Relevant diffs trigger full
configured analysis; KUnit coverage follows the actual build
configuration.

Retain build logs, compilation databases, native XML and checker
coverage. Separate source findings from parser failures, missing inputs
and incomplete builds, with isolated report and capture fixtures.

scripts/policy/cppcheck.json

@@ -0,0 +1,9 @@
+{
+  "version": 1,
+  "notes": [
+    "Capture fresh kernel CHECK and userspace compiler commands.",
+    "Analyze configured translation units with native headers and definitions.",
+    "KUNIT_TEST=y includes KUnit sources through their actual Kbuild context.",
+    "No project models, inline suppressions or diagnostic exceptions."
+  ]
+}