bug#19111: 25.0.50; 32 bits temacs.exe is linked with wrong image-base when built on 64 bit Windows host

[Eli Zaretskii]

> From: Óscar Fuentes <ofv@wanadoo.es>
> Cc: 19111@debbugs.gnu.org
> Date: Wed, 19 Nov 2014 22:27:30 +0100
> 
> The problem here is that, without explicitly setting --host/--build,
> uname is not the right thing for detecting the host/build environment,
> because uname is a MSYS2 thing, when we are building with a MinGW
> toolset. So either we stop using uname for MinGW builds (use $MSYSTEM),
> or document that --host/--build are required.

When you use MinGW64 for building a 32-bit executable, you are in
effect cross-compiling.  So I think telling users to use an explicit
"--host/--build" argument is TRT, especially since I don't envision
many people doing that, except for special-case testing.

Patches for nt/INSTALL are welcome.

Thanks.