Try to get things working again with Bazel 7.

Specifically, try passing `--platforms` as well as `--cpu`.
(The latter is going away eventually, but keep it for now.)

Change-Id: Id53ba7b91008c7b90b1e9d242a3eded3e65007b8
Reviewed-on: https://code-review.googlesource.com/c/re2/+/62370
Reviewed-by: Paul Wankadia <junyer@google.com>
Reviewed-by: Alex Chernyakhovsky <achernya@google.com>