Use new Severity class and update *_warn_patterns

* This new class definition and patterns are
  shared between Android and ChromeOS compiler tools.
* Suppress hard to fix and false positive linter warnings.

Test: warn.py --url=http://cs/android --separator='?l=' build.log > warnings.html
Test: warn.py --gencsv build.log > warnings.csv
Change-Id: Icb47809100ad30796cb1da82610e989d450194fa

tools/warn/make_warn_patterns.py

@@ -1,4 +1,4 @@
-#
+# python3
 # Copyright (C) 2019 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
@@ -15,9 +15,12 @@
 
 """Warning patterns for build make tools."""
 
-from severity import Severity
+# pylint:disable=relative-beyond-top-level
+from .cpp_warn_patterns import compile_patterns
+# pylint:disable=g-importing-member
+from .severity import Severity
 
-patterns = [
+warn_patterns = [
     # pylint:disable=line-too-long,g-inconsistent-quotes
     {'category': 'make', 'severity': Severity.MEDIUM,
      'description': 'make: overriding commands/ignoring old commands',
@@ -51,3 +54,6 @@ patterns = [
      'description': 'make: please convert to soong',
      'patterns': [r".*: warning: .* has been deprecated. Please convert to Soong."]},
 ]
+
+
+compile_patterns(warn_patterns)