Unable to build GDB on Windows

[Eli Zaretskii]

> Date: Mon, 28 Sep 2020 08:15:23 -0700
> From: Joel Brobecker <brobecker@adacore.com>
> 
> > Btw, looking at Gnulib's getrandom.c, my conclusion is that a GDB
> > built on Windows 7 and later will be unable to run on older versions
> > of Windows, because it will have a static dependency on bcrypt.dll and
> > the BCryptGenRandom function from that DLL.  IOW, such a GDB will
> > refuse to run on older Windows systems.
> 
> I think that's fine. IMO, the general spirit should be that people
> interested in building a GDB that works on multiple versions of
> an OS should build it on the oldest version they want to support.
> I don't think we want to commit to anything stronger than that.

Maybe just say that in some README?