Add in-kernel test runner

This adds a way to run tests inside the Smalltown kernel.

Improvements to the Bazel part of this are tracked in T726

Test Plan: Tested by intentionally failing the test.

X-Origin-Diff: phab/D485
GitOrigin-RevId: e4aad7f28d122d82a7fcb6699e678cbe022e2f73
diff --git a/third_party/linux/BUILD.bazel b/third_party/linux/BUILD.bazel
index 3829f96..48f811b 100644
--- a/third_party/linux/BUILD.bazel
+++ b/third_party/linux/BUILD.bazel
@@ -20,3 +20,9 @@
     """,
     visibility = ["//visibility:public"],
 )
+
+filegroup(
+    name = "kernel-config",
+    srcs = ["linux-smalltown.config"],
+    visibility = ["//visibility:public"],
+)