doc/platform: Add info on shared builds with MSVC

Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

doc/platform.texi

@@ -104,7 +104,7 @@ you can build all libraries as DLLs.
 @section Microsoft Visual C++
 
 Libav can be built with MSVC using a C99-to-C89 conversion utility and
-wrapper. At this time, only static builds are supported.
+wrapper.
 
 You will need the following prerequisites:
 
@@ -120,8 +120,8 @@ you want to run @uref{fate.html, FATE}.
 To set up a proper MSVC environment in MSYS, you simply need to run
 @code{msys.bat} from the Visual Studio command prompt.
 
-Place @code{c99wrap.exe}, @code{c99conv.exe}, and @code{yasm.exe} somewhere
-in your @code{PATH}.
+Place @code{makedef}, @code{c99wrap.exe}, @code{c99conv.exe}, and @code{yasm.exe}
+somewhere in your @code{PATH}.
 
 Next, make sure @code{inttypes.h} and any other headers and libs you want to use
 are located in a spot that MSVC can see. Do so by modifying the @code{LIB} and
@@ -137,6 +137,11 @@ make
 make install
 @end example
 
+If you wish to compile static libraries, add @code{--enable-shared} to your
+configure options. Note that due to the way MSVC handles DLL imports and
+exports, you cannot compile static and shared libraries at the same time, and
+enabling shared libraries will automatically disable the static ones.
+
 Notes:
 
 @itemize