Update Makefile

Makefile

@@ -17,20 +17,31 @@ Makefile.coq: _CoqProject Makefile
 	"$(COQBIN)coq_makefile" -f _CoqProject -o Makefile.coq
 
 # Install build-dependencies
-build-dep/opam: opam Makefile
-	@echo "# Creating build-dep package."
-	@mkdir -p build-dep
-	@sed <opam -E 's/^(build|install|remove):.*/\1: []/; s/^name: *"(.*)" */name: "\1-builddep"/' >build-dep/opam
-	@fgrep builddep build-dep/opam >/dev/null || (echo "sed failed to fix the package name" && exit 1) # sanity check
-
-build-dep: build-dep/opam phony
-	@# We want opam to not just instal the build-deps now, but to also keep satisfying these
+OPAMFILES=$(wildcard *.opam)
+BUILDDEPFILES=$(addsuffix -builddep.opam, $(addprefix builddep/,$(basename $(OPAMFILES))))
+
+builddep/%-builddep.opam: %.opam Makefile
+	@echo "# Creating builddep package for $<."
+	@mkdir -p builddep
+	@sed <$< -E 's/^(build|install|remove):.*/\1: []/; s/"(.*)"(.*= *version.*)$$/"\1-builddep"\2/;' >$@
+
+builddep-opamfiles: $(BUILDDEPFILES)
+.PHONY: builddep-opamfiles
+
+builddep: builddep-opamfiles
+	@# We want opam to not just install the build-deps now, but to also keep satisfying these
 	@# constraints.  Otherwise, `opam upgrade` may well update some packages to versions
 	@# that are incompatible with our build requirements.
 	@# To achieve this, we create a fake opam package that has our build-dependencies as
 	@# dependencies, but does not actually install anything itself.
-	@echo "# Installing build-dep package."
-	@opam install $(OPAMFLAGS) build-dep/
+	@echo "# Installing builddep packages."
+	@opam install $(OPAMFLAGS) $(BUILDDEPFILES)
+.PHONY: builddep
+
+# Backwards compatibility target
+build-dep: builddep
+.PHONY: build-dep
+
 
 # Some files that do *not* need to be forwarded to Makefile.coq
 Makefile: ;