Scudo tests in compiler-rt/test/scudo are not run

While looking at `compiler-rt` tests that use `-shared-lib*san`, I noticed that the Scudo tests in `compiler-rt/test/scudo` are not built or run, unlike their counterparts in `compiler-rt/test/scudo/standalone`.

AFAICT this directory lacks a `CMakeLists.txt` file that would introduce a `check-scudo` target.