Build the Clang plugin on Windows.

tools/clang/plugins/FindBadConstructsConsumer.cpp

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "FindBadConstructsConsumer.h"
 
 #include "clang/Frontend/CompilerInstance.h"
 #include "clang/AST/Attr.h"
 #include "clang/Lex/Lexer.h"
 #include "llvm/Support/raw_ostream.h"
@@ skipping 541 matching lines @@
       return PublicDestructor;
     }
   }
 
   return None;
 }
 
 // Adds either a warning or error, based on the current handling of
 // -Werror.
 DiagnosticsEngine::Level FindBadConstructsConsumer::getErrorLevel() {
+#ifdef LLVM_ON_WIN32
+  // Only warn on Windows, since there are a lot of potential pre-existing
+  // issues.
+  return DiagnosticsEngine::Warning;
+#else
   return diagnostic().getWarningsAsErrors() ? DiagnosticsEngine::Error
                                             : DiagnosticsEngine::Warning;
+#endif
 }
 
 // Returns true if |base| specifies one of the Chromium reference counted
 // classes (base::RefCounted / base::RefCountedThreadSafe).
 bool FindBadConstructsConsumer::IsRefCountedCallback(
     const CXXBaseSpecifier* base,
     CXXBasePath& path,
     void* user_data) {
   FindBadConstructsConsumer* self =
       static_cast<FindBadConstructsConsumer*>(user_data);
@@ skipping 213 matching lines @@
     // one of those, it means there is at least one member after a factory.
     if (weak_ptr_factory_location.isValid() &&
         !param_is_weak_ptr_factory_to_self) {
       diagnostic().Report(weak_ptr_factory_location,
                           diag_weak_ptr_factory_order_);
     }
   }
 }
 
 }  // namespace chrome_checker