bug#28601: 26.0.50; configure: error: Emacs does not support 'x86_64-pc-msys' systems.

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Date: Thu, 12 Oct 2017 19:06:56 -0400
> Cc: Andy Moreton <andrewjmoreton@gmail.com>, 28601@debbugs.gnu.org, 
>       Vincent Belaïche <vincent.belaiche@gmail.com>
> 
> -First we need to switch to the MinGW-w64 environment.  Exit the MSYS2 BASH
> -console and run mingw64_shell.bat in the C:\msys64 folder, then cd back to
> +First we need to switch to the MinGW-w64 environment.  Exit the MSYS2
> +BASH console and run mingw64.exe in the C:\msys64 folder (if it's
> +missing, install it with 'pacman -S msys2-launcher'), then cd back to
>  your Emacs source directory, e.g.:

Can we rely on all the users to have the latest MSYS2?  If not,
perhaps after your description we should say something like "If you
don't have mingw64.exe, but do have mingw64_shell.bat, then ..."?

Thanks.