lint: Add exclusions for libmultiprocess subtree

Without this change linter produces errors about:

- Use of std::filesystem the libmultiprocess example program.
- Use of locale-dependent functions in example program, in the build time code
  generator, and in the runtime library for debug logging.
- Include guards not beginning with BITCOIN_

test/lint/lint-locale-dependence.py

@@ -51,6 +51,7 @@ KNOWN_VIOLATIONS = [
 
 REGEXP_EXTERNAL_DEPENDENCIES_EXCLUSIONS = [
     "src/crypto/ctaes/",
+    "src/ipc/libmultiprocess/",
     "src/leveldb/",
     "src/secp256k1/",
     "src/minisketch/",