Makefile.common: fix promu download path for arm32 (#4998)

Signed-off-by: Paul Gier <pgier@redhat.com>

Makefile.common

@@ -62,8 +62,14 @@ PROMU        := $(FIRST_GOPATH)/bin/promu
 STATICCHECK  := $(FIRST_GOPATH)/bin/staticcheck
 pkgs          = ./...
 
-GO_VERSION        ?= $(shell $(GO) version)
-GO_BUILD_PLATFORM ?= $(subst /,-,$(lastword $(GO_VERSION)))
+GOHOSTOS ?= $(shell $(GO) env GOHOSTOS)
+GOHOSTARCH ?= $(shell $(GO) env GOHOSTARCH)
+ifeq (arm, $(GOHOSTARCH))
+	GOHOSTARM ?= $(shell GOARM= $(GO) env GOARM)
+	GO_BUILD_PLATFORM ?= $(GOHOSTOS)-$(GOHOSTARCH)v$(GOHOSTARM)
+else
+	GO_BUILD_PLATFORM ?= $(GOHOSTOS)-$(GOHOSTARCH)
+endif
 
 PROMU_VERSION ?= 0.2.0
 PROMU_URL     := https://github.com/prometheus/promu/releases/download/v$(PROMU_VERSION)/promu-$(PROMU_VERSION).$(GO_BUILD_PLATFORM).tar.gz