doc/platform: Reference only MSYS2 and MinGW-w64

It's better to steer users at these, since they are both better
and more alive than the mingw.org versions.
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>

doc/platform.texi

@@ -91,9 +91,9 @@ For information about compiling Libav on OS/2 see
 
 @section Native Windows compilation using MinGW or MinGW-w64
 
-Libav can be built to run natively on Windows using the MinGW or MinGW-w64
-toolchains. Install the latest versions of MSYS and MinGW or MinGW-w64 from
-@url{http://www.mingw.org/} or @url{http://mingw-w64.sourceforge.net/}.
+Libav can be built to run natively on Windows using the MinGW-w64
+toolchain. Install the latest versions of MSYS2 and MinGW-w64 from
+@url{http://msys2.github.io/} and/or @url{http://mingw-w64.sourceforge.net/}.
 You can find detailed installation instructions in the download section and
 the FAQ.
 
@@ -101,7 +101,7 @@ Notes:
 
 @itemize
 
-@item Building natively using MSYS can be sped up by disabling implicit rules
+@item Building natively using MSYS2 can be sped up by disabling implicit rules
 in the Makefile by calling @code{make -r} instead of plain @code{make}. This
 speed up is close to non-existent for normal one-off builds and is only
 noticeable when running make for a second time (for example during
@@ -127,13 +127,14 @@ You will need the following prerequisites:
 (if using MSVC 2012 or earlier)
 @item @uref{http://code.google.com/p/msinttypes/, msinttypes}
 (if using MSVC 2012 or earlier)
-@item @uref{http://www.mingw.org/, MSYS}
+@item @uref{http://msys2.github.io/, MSYS2}
 @item @uref{http://yasm.tortall.net/, YASM}
+(Also available via MSYS2's package manager.)
 @item @uref{http://gnuwin32.sourceforge.net/packages/bc.htm, bc for Windows} if
 you want to run @uref{fate.html, FATE}.
 @end itemize
 
-To set up a proper environment in MSYS, you need to run @code{msys.bat} from
+To set up a proper environment in MSYS2, you need to run @code{msys_shell.bat} from
 the Visual Studio or Intel Compiler command prompt.
 
 Place @code{yasm.exe} somewhere in your @code{PATH}. If using MSVC 2012 or