Reworking the MSVC-related build options

[Tor Lillqvist]

BTW, as you no doubt will notice, we got a patch in from Peter Foley
through gerrit that does the kill-oowintool aspect of what I was
working on, great! That already cleans up things quite a bit.

Now just the reduce-unnecessary-options part is left to do, and
perhaps some tweaking of preference in compilers, and especially in
what .NET Framework to use.

I yesterday noticed that installing on a vanilla XP SP3 fails if you
have managed code built with the 4 framework, so probably we need to
make sure to build our CLI stuff with version 2 of the framework? Is
it enough to use the v2.0.foo csc.exe (which is always present, I
think?), or do we need to find an older al.exe, too? Not totally clear
to me. At least, we should give a warning from configure if building
with "too new" .NET tools, warn that a thusly built LO should not be
distributed to the public as it won't necessarily install on XP.

--tml