Use `PUBLIC_HEADER` to install headers.

Change-Id: I8d7a1b51deb35773d95af2ec1b7a866c8700f0d7
Reviewed-on: https://code-review.googlesource.com/c/re2/+/61030
Reviewed-by: Alex Chernyakhovsky <achernya@google.com>
Reviewed-by: Paul Wankadia <junyer@google.com>
1 file changed