Get `gn gen` to succeed on Windows

1. Pull in NSS for net, crypto
2. Copy sqlite from chromium for NSS
3. Some mucking in build/ to avoid DEPSing gyp
4. Pull in gperf and bison on win

I believe 1&2 can be deleted later once net is moved out.

This gets as far as successful project generation, and builds a bunch
of stuff but there's still quite a few compile errors.

Result of `ninja -C out\Debug root -k0 >log.txt` here:
https://gist.github.com/sgraham/7e58a022595db1c0ae60

They don't look too major, but I don't know if mojo wants to take on
longer term support/maintenance of Windows, with bots/etc. so not sure
this is worth it or not.

(To work fully this also requires a ninja binary at ninja ToT that's
not pushed to depot_tools yet. But the compile errors are unrelated,
and ninja will get there eventually.)

R=jam@chromium.org
BUG=

Review URL: https://codereview.chromium.org/694353003