Add script for building majokko binaries for multiple platforms.

.gitignore

@@ -1,4 +1,9 @@
+dist/
 majokko
 test.png
 test.zng
 test.jpg
+test.ppm
+test.bmp
+test.tif
+test.tga

build_cross.sh

@@ -0,0 +1,18 @@
+#!/bin/sh
+GO="${GO:-go}"
+LDFLAGS="${LDFLAGS:--w -s}"
+
+echo "Using:"
+echo "GO='$GO'"
+echo "LDFLAGS='$LDFLAGS'"
+echo ""
+
+mkdir -p dist/
+for cpu in amd64 386 arm arm64; do
+  for os in windows linux darwin; do
+    DISTFILE="dist/majokko-${os}-${cpu}"
+    CMD="GOOS='${os}' GOARCH='${cpu}' ${GO} build -o '$DISTFILE' -ldflags '$LDFLAGS' -trimpath ."
+    echo "= $CMD"
+    eval "$CMD" && echo "+ $(du -hs "$DISTFILE")" || echo "- Error: ${os} on ${cpu}"
+  done
+done