Try again to make cross-compiling on Windows work.

Change-Id: I620e5f48642454572a2187ce0532c2b333603389
Reviewed-on: https://code-review.googlesource.com/c/re2/+/61613
Reviewed-by: Alex Chernyakhovsky <achernya@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>