Build in msys2 shell fails

[Gene Smith]

Installed msys2 on window 10 as recommended. The various "pacman" steps 
were not quite as straight forward as described on the msys2 website. 
However, I think I got it installed OK and it runs and all packages are 
up to date (including the additional packages required by RSB). Also 
installed the windows version of python2.

However, when I run (in MSYS shell) a build with the same command line 
as on cygwin or linux but with the added options --without-python and 
--jobs=none, I immediately see this:

error: failed to load Windows host support

This is coming from builder file .../sb/options.py and indicates that it 
thinks the "os.name" is "nt".

I tried installing and using python3 and see the same thing.

Also, running a MINGW64 shell does the same thing with both python 
versions. (No path entries to cygwin code are present.)

Am I doing something wrong? (Haven't tried the msys python package which 
the documentation says doesn't work with RSB.)

-gene