CI: Faster builds with buildx and xcputranslate

Dockerfile

@@ -1,7 +1,7 @@
 ARG ALPINE_VERSION=3.12
 ARG GO_VERSION=1.15
 
-FROM golang:${GO_VERSION}-alpine${ALPINE_VERSION} AS base
+FROM --platform=$BUILDPLATFORM golang:${GO_VERSION}-alpine${ALPINE_VERSION} AS base
 RUN apk --update add git
 ENV CGO_ENABLED=0
 WORKDIR /tmp/gobuild
@@ -10,25 +10,29 @@ RUN go mod download
 COPY cmd/ ./cmd/
 COPY internal/ ./internal/
 
-FROM base AS test
+FROM --platform=$BUILDPLATFORM base AS test
 ENV CGO_ENABLED=1
 RUN apk --update add g++
 RUN go test -race ./...
 
-FROM base AS lint
+FROM --platform=$BUILDPLATFORM base AS lint
 ARG GOLANGCI_LINT_VERSION=v1.34.1
 RUN wget -O- -nv https://raw.githubusercontent.com/golangci/golangci-lint/master/install.sh | \
     sh -s -- -b /usr/local/bin ${GOLANGCI_LINT_VERSION}
 COPY .golangci.yml ./
 RUN golangci-lint run --timeout=10m
 
-FROM base AS build
+FROM --platform=$BUILDPLATFORM base AS build
+COPY --from=qmcgaw/xcputranslate /xcputranslate /usr/local/bin/xcputranslate
+ARG TARGETPLATFORM
 ARG VERSION=unknown
 ARG BUILD_DATE="an unknown date"
 ARG COMMIT=unknown
 COPY cmd/ ./cmd/
 COPY internal/ ./internal/
-RUN go build -trimpath -ldflags="-s -w \
+RUN GOARCH="$(echo ${TARGETPLATFORM} | xcputranslate -field arch)" \
+    GOARM="$(echo ${TARGETPLATFORM} | xcputranslate -field arm)" \
+    go build -trimpath -ldflags="-s -w \
     -X 'main.version=$VERSION' \
     -X 'main.buildDate=$BUILD_DATE' \
     -X 'main.commit=$COMMIT' \