[CM] a short guide on compile on msys2/windows with cload.scm

[x.x. chai]

Hi,

1. The functions lacking in libc.scm on msys2 are the following:

gethostent, setnetent, endnetent, getnetent, getnetbyname, getnetbyaddr 

2. 
> We need to make up our minds -- is msys2 actually different from mingw?  If
> not,
> let's use mingw64 as the compile time switch, not msys.

MINGW64 is different from MSYS2, yes. MSYS2 have more functions
available for one, I guess. For example, MSYS2 has `realpath', 
but MINGW64 does not have. In order to compile s7 under MINGW64, 
one needs to write a lot of extra code.

It would be nice of course to compile s7 on MINGW64. It will
take a lot of your energy. As a selfish user, I would suggest
working on other aspects first.