Type: LanguageService

Describe the bug

• OS and Version: Windows 10 (but shouldn't be version specific)
• VS Code Version: 1.30.1 (but shouldn't be version specific)
• C/C++ Extension Version: 0.20.1 (but shouldn't be version specific)
• Other extensions you installed (and if the issue persists after disabling them): N/A
• A clear and concise description of what the bug is:

In cl.exe, C++/CX is enabled using the /ZW flag. There is at present no facility to enable this from IntelliSense perspective in the cpptools extension.

There are some approaches to this:

• allow a --cppcx flag on the compilerPath, similar to /clr (see C++ CLI support for assembly references #1987).
• allow a generic compilerFlags field to specify arbitrary compiler flags, one of which could be /ZW, which then gets translated to the relevant EDG setting.

To Reproduce
Set up a C++/CX project

Expected behavior
C++/CX constructs are supported