Faster multi stage build using cross compilation (#72)

Co-authored-by: maddie <maddie@users.noreply.github.com>

Dockerfile

@@ -1,11 +1,13 @@
-FROM golang:1.18-alpine AS build_base
+FROM --platform=$BUILDPLATFORM golang:1.18-alpine AS build_base
 RUN apk add --no-cache git gcc ca-certificates libc-dev
 WORKDIR /build
 COPY go.mod go.sum ./
 RUN go mod download
 COPY ./ ./
+
 ENV CGO_ENABLED=0
-RUN go build -ldflags "-w -s" -trimpath -o speedtest .
+ARG TARGETOS TARGETARCH
+RUN GOOS=$TARGETOS GOARCH=$TARGETARCH go build -ldflags "-w -s" -trimpath -buildvcs=false -o speedtest .
 
 FROM scratch
 WORKDIR /app