Support repositories with mutliple opam files

prepare-opam.sh

@@ -48,12 +48,18 @@ test -d "$OPAMROOT/repo/iris-dev" || opam repo add iris-dev https://gitlab.mpi-s
 opam repo prio iris-dev 1 # make sure this stays at the top
 echo
 
-# Make sure the the builddep package exists and is up-to-date.
-make build-dep/opam
+# Make sure the the builddep package(s) exist and are up-to-date.
+if test -f opam; then
+    # Old-style package: a single opam file
+    make build-dep/opam
+else
+    # New-style package has a dedicated target to just generate the files
+    make build-dep-opamfiles
+fi
 
 # Update old opam, if we got a cache.
 if [[ -z "$FRESH_OPAM" ]]; then # skip if this is a fresh opam root
-    # Update repositories and reinit.  build-dep/opam must exist here because it
+    # Update repositories and reinit.  build-dep/* must exist here because it
     # might be installed, and opam would complain if it had went missing.
     opam init --no-setup --disable-sandboxing --reinit -y
     # We need `opam update` anyway to update git branches.