Extract WebP building into a script

builder/scripts/build-webp

@@ -0,0 +1,23 @@
+#!/usr/bin/env bash
+
+set -euo pipefail
+
+webp_tar_url=https://storage.googleapis.com/downloads.webmproject.org/releases/webp/libwebp-1.0.2.tar.gz
+
+prepare_source() {
+  cd /tmp
+  wget "$webp_tar_url"
+  tar -xzf /tmp/libwebp-*
+  rm /tmp/libwebp-*.tar.gz
+  cd /tmp/libwebp-*
+}
+
+build_and_install() {
+  export MAKEFLAGS=-j`nproc`
+  ./configure --enable-static --disable-shared
+  make
+  make install
+}
+
+prepare_source
+build_and_install