build: force Docker-owned compilation

Makefile

@@ -43,13 +43,13 @@ docker-image: Dockerfile
 	docker build -t $(DOCKER_IMAGE) - < Dockerfile
 
 docker-build:
-	$(DOCKER_RUN) make all
+	$(DOCKER_RUN) make -B all
 
 docker-check:
-	$(DOCKER_RUN) make check TESTARGS="$(TESTARGS)"
+	$(DOCKER_RUN) make -B check TESTARGS="$(TESTARGS)"
 
 docker-bench:
-	$(DOCKER_RUN) make bench
+	$(DOCKER_RUN) make -B bench
 
 docker: docker-image
 	$(MAKE) docker-build

README.md

@@ -60,7 +60,9 @@ make docker-check
 
 `docker-image` creates the Arch Linux dependency image, `docker-build`
 compiles the runtime components, and `docker-check` runs the map verifiers and
-test suites.  `docker` is a convenience alias for the image and build steps.
+test suites.  Docker targets force their own compilation, so newer host
+objects cannot be reused.  `docker` is a convenience alias for the image and
+build steps.
 The resulting runtime artifacts are:
 
 ```text