PSA: Changes to embedding Python Windows incoming

If you don’t build LLDB on Windows, you can stop reading now.

I’ve just uploaded http://reviews.llvm.org/D8979 for review, which is going to change the way people build on Windows (for the better).

I plan to commit it later today, but I wanted to give people a heads up in case they don’t closely follow the commits list that this will be incoming.

The TL;DR of the review description is that after this patch:
a) You will only need to specify 1 CMake variable instead of 3
b) You can clear your PYTHONPATH and PYTHONHOME variables and everything will still work for every combination of {Debug,Release} x {x64,x86}