message: Update docs for VS2017 configuration
diff: @@ -174,16 +174,16 @@ cmake -DCMAKE_BUILD_TYPE=Release -DBSONCXX_POLY_USE_BOOST=1 \
  ```
  On Windows, here's an example of how to configure for MSVC (assuming
  -libmongoc and libbson are in `c:\mongo-c-driver` as given in the
  +libmongoc and libbson are in `C:\mongo-c-driver` as given in the
  [mongoc Windows installation
  instructions](http://mongoc.org/libmongoc/current/installing.html#building-windows)
  and boost is in `c:\local\boost_1_59_0`:
  ```sh
  -'C:\Program Files (x86)\CMake\bin\cmake.exe' -G "Visual Studio 14 Win64"
  +'C:\Program Files (x86)\CMake\bin\cmake.exe' -G "Visual Studio 14 2015 Win64"
  -DCMAKE_INSTALL_PREFIX=C:\mongo-cxx-driver
  - -DCMAKE_PREFIX_PATH=c:\mongo-c-driver
  - -DBOOST_ROOT=c:\local\boost_1_59_0 ..
  + -DCMAKE_PREFIX_PATH=C:\mongo-c-driver
  + -DBOOST_ROOT=C:\local\boost_1_59_0 ..
  ```
  `mongocxx` builds shared libraries by default. This is the recommended
  @@ -196,6 +196,16 @@ build setting for novice users.
  shared `libmongoc` and static `mongocxx` is not supported, nor is
  linking against both static `libmongoc` and shared `mongocxx`.
  +For building with Visual Studio 2017 (without a C++17 polyfill), it is necessary to configure with an additional option, "/Zc:__cplusplus" to opt into the correct definition of `__cplusplus` ([problem described here](https://blogs.msdn.microsoft.com/vcblog/2018/04/09/msvc-now-correctly-reports-__cplusplus/)):
  +
  +```sh
  +'C:\Program Files (x86)\CMake\bin\cmake.exe' -G "Visual Studio 15 2017 Win64"
  + -DCMAKE_INSTALL_PREFIX=C:\mongo-cxx-driver
  + -DCMAKE_PREFIX_PATH=C:\mongo-c-driver
  + -DCMAKE_CXX_STANDARD=17
  + -DCMAKE_CXX_FLAGS="/Zc:__cplusplus" ..
  +```
  +
  ### Step 5: Build and install the driver
  If you are using the default MNMLSTC polyfill and are installing to a
  