How is mā best interpreted after idhā here?

Imruʾ al-Qays: Dialogue in ʿUnayzah’s Litter, Boasting, and an Oath (Verses 13–18)

• The subject of bakā
• An emphatic/pleonastic mā, not necessarily a relative pronoun
• The predicate of inṣarafat
• The second term of an iḍāfah