Use buildx to support multiarch images

Makefile

@@ -4,7 +4,7 @@ TAGS ?= 81 81-fpm 81-unit 82 82-fpm 82-unit
 COMPOSER_HASH ?= 55ce33d7678c5a611085589f1f3ddf8b3c52d662cd01d4ba75c0ee0459970c2200a51f492d557530c71c15d8dba01eae
 DRUSH_VERSION ?= 8.4.12
 DOCKER_BUILDKIT ?= 1
-PLATFORM ?= linux/amd64
+PLATFORM ?= linux/amd64,linux/arm64
 
 .PHONY: all build push
 
@@ -14,7 +14,6 @@ build:
 	@echo "Building images for tags: $(TAGS)"
 	set -e; for i in $(TAGS); do printf "\nBuilding $(NAME):$$i \n\n"; cd php$$i; \
 		DOCKER_BUILDKIT=$(DOCKER_BUILDKIT) docker build -t $(NAME):$$i \
-		--platform $(PLATFORM) \
 		--no-cache --progress=plain \
 		--build-arg COMPOSER_HASH=$(COMPOSER_HASH) \
 		--build-arg DRUSH_VERSION=$(DRUSH_VERSION) \
@@ -28,3 +27,15 @@ push:
 
 unit:
 	make -C unit-php-builder/dev build
+
+buildx-push:
+	@echo "Building images for tags: $(TAGS)"
+		set -e; for i in $(TAGS); do printf "\nBuilding $(NAME):$$i \n\n"; cd php$$i; \
+		docker buildx build -t $(NAME):$$i --push \
+		--platform $(PLATFORM) \
+		--no-cache --progress=plain \
+		--build-arg COMPOSER_HASH=$(COMPOSER_HASH) \
+		--build-arg DRUSH_VERSION=$(DRUSH_VERSION) \
+		--build-arg BUILD_DATE=`date -u +"%Y-%m-%dT%H:%M:%SZ"` \
+		--build-arg VCS_REF=`git rev-parse --short HEAD` .; \
+		cd ..; done