Add system include path support for pre-VS2015 compilers

I'm trying to get my Windows set up to work properly, but at the moment I get errors saying it can't find source files even though I can control+click on the files and open them.

Config:

{
    "configurations": [
        {
            "name": "Win32",
            "includePath": [
                "C:\\Program Files (x86)\\Microsoft Visual Studio 10.0\\VC\\include",
                "C:/Users/nscott/workspace/asldev/aslcore/",
                "C:/Users/nscott/workspace/qt4/qt4/include"
            ],
            "browse": {
                "limitSymbolsToIncludedHeaders": true,
                "databaseFilename": "",
                "path": [
                    "C:/Program Files (x86)/Microsoft Visual Studio 10.0/VC/include/",
                    "C:/Users/nscott/workspace/asldev/aslcore/",
                    "C:/Users/nscott/workspace/qt4/qt4/include",
                    "${workspaceRoot}"
                ]
            },
            "defines": [
                "_DEBUG",
                "UNICODE"
            ],
            "intelliSenseMode": "msvc-x64",
            "compileCommands": "C:\\w\\build_x86_debug\\compile_commands.json"
        }
    ],
    "version": 4
}

Start by reproducing the Windows configuration with a pre-VS2015 compiler, focusing on how includePath, browse.path, and compileCommands are interpreted. Trace the C/C++ extension entry point that resolves system headers and compare behavior for the Visual Studio 10.0 include directory; done means those headers resolve without source-file errors.