Windows SDK includes need to be lowercase for MinGW builds. Bug: angleproject:3336 Change-Id: If2075b3ed2fe0be95ab2ec9cd0398afef691dee8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1548433 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Jamie Madill <jmadill@chromium.org>