Upgrade Oniguruma to 6.9.7 revised 1

Summary:
The version is tagged 6.9.7.1 but the archive directory is 6.9.7.
To avoid to maintain two version numbers, this change extracts
the source code to /usr/src/onigurama regardless of the version.

Test Plan: Build image

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2518