[recipes] Fix Windows pathsep; add Windows tests

Change-Id: Ie74bc321dcd1a9150b55b36278e94acf1df34139
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/210220
Commit-Queue: Eric Boren <borenet@google.com>
Auto-Submit: Ben Wagner aka dogben <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
27 files changed