mirage/mirage: PR #1527: fix generated opam file - the build rule is now `make "-Csubdir" "build"

@4ba1423

Stages:

• 🟡 x86_64-debian-10-4.13
• ✔️ arm64-debian-10-4.13 (5m51s)

History:

• 17/05/2024 10:37 🟡 @aff5e9f (7m15s)
• 09/05/2024 19:02 ✔️ @6175e46 (6h36m)
• 06/05/2024 18:16 🟡 @4ba1423 (5m51s)