Add new clang-tidy and clang warning patterns

* New "clang-tidy used ... seconds" warnings are reported when
  clang-tidy runs for more than 1/2 of TIDY_TIMEOUT seconds.
* Recognize other clang-tidy warnings in separate groups;
  they should not be used in normal Android builds.
* Add two more variants of C++ warnings.

Test: warn.py --url=http://cs/android --separator='?l=' build.log > warnings.html
Test: warn.py --gencsv build.log > warnings.csv
Change-Id: I4a2e1c3c817c586cfe3da125b920cca77fcc63b6

tools/warn/cpp_warn_patterns.py

@@ -297,6 +297,7 @@ warn_patterns = [
            [r".*: warning: declaration 'class .+' does not declare anything"]),
     medium('Initialization order will be different',
            [r".*: warning: '.+' will be initialized after",
+            r".*: warning: initializer order does not match the declaration order",
             r".*: warning: field .+ will be initialized after .+Wreorder"]),
     skip('skip,   ....',
          [r".*: warning:   '.+'"]),
@@ -448,6 +449,7 @@ warn_patterns = [
            [r".*: warning: 'operator new' must not return NULL unless it is declared 'throw\(\)' .+"]),
     medium('NULL used in arithmetic',
            [r".*: warning: NULL used in arithmetic",
+            r".*: warning: .* subtraction with a null pointer",
             r".*: warning: comparison between NULL and non-pointer"]),
     medium('Misspelled header guard',
            [r".*: warning: '.+' is used as a header guard .+ followed by .+ different macro"]),