build: fix multiarch build

TARGETPLATFORM must not have a default value.

Makefile

@@ -20,8 +20,7 @@ endif
 
 BUILD_ARGS := \
 	--build-arg JITSI_REPO=$(JITSI_REPO) \
-	--build-arg JITSI_RELEASE=$(JITSI_RELEASE) \
-	--build-arg TARGETPLATFORM=$(TARGETPLATFORM)
+	--build-arg JITSI_RELEASE=$(JITSI_RELEASE)
 
 ifeq ($(FORCE_REBUILD), 1)
   BUILD_ARGS := $(BUILD_ARGS) --no-cache
@@ -61,7 +60,7 @@ build:
 else
 build:
 	@echo "Building for $(TARGETPLATFORM)"
-	docker build $(BUILD_ARGS) --progress plain --tag $(JITSI_REPO)/$(JITSI_SERVICE) $(JITSI_SERVICE)/
+	docker build $(BUILD_ARGS) --build-arg TARGETPLATFORM=$(TARGETPLATFORM) --progress plain --tag $(JITSI_REPO)/$(JITSI_SERVICE) $(JITSI_SERVICE)/
 endif
 
 $(addprefix build_,$(JITSI_SERVICES)):

jibri/Dockerfile

@@ -12,7 +12,7 @@ RUN apt-dpkg-wrap apt-get update && \
     apt-dpkg-wrap apt-get install -y jibri libgl1-mesa-dri procps jitsi-upload-integrations jq && \
     apt-cleanup
 
-ARG TARGETPLATFORM=unset
+ARG TARGETPLATFORM
 ARG USE_CHROMIUM=0
 #ARG CHROME_RELEASE=latest
 #ARG CHROMEDRIVER_MAJOR_RELEASE=latest