makefile: move dockerexec to helper, bind GOCACHE/GOMODCACHE by env

Makefile

@@ -2,6 +2,19 @@ BUILDSTAMPS := docker/genbindings.docker-buildstamp
 DOCKER := docker
 SHELL := /bin/bash
 
+# DOCKEREXEC runs the target command in the `genbindings` docker container.
+# It mounts in the current GOCACHE and GOMODCACHE.
+DOCKEREXEC = mkdir -p "$$(go env GOCACHE)" && \
+	mkdir -p "$$(go env GOMODCACHE)" && \
+	$(DOCKER) run \
+	--user "$$(id -u):$$(id -g)" \
+	-v "$$(go env GOCACHE):/.cache/go-build" \
+	-v "$$(go env GOMODCACHE):/go/pkg/mod" \
+	-v "$$PWD:/src" \
+	-w /src \
+	miqt/genbindings:latest \
+	/bin/bash -c
+
 .PHONY: all
 all: genbindings
 
@@ -16,6 +29,5 @@ clean:
 
 .PHONY: genbindings
 genbindings: $(BUILDSTAMPS)
-	mkdir -p ~/.cache/go-build
+	$(DOCKEREXEC) 'cd cmd/genbindings && go build && ./genbindings'
-	$(DOCKER) run --user $$(id -u):$$(id -g) -v ~/.cache/go-build:/.cache/go-build -v $$PWD:/src -w /src miqt/genbindings:latest /bin/bash -c 'cd cmd/genbindings && go build && ./genbindings'