Separate build script from install script #4458

The --build-from-source flag is now deprecated and will soon
be removed along with the need to define an install script.

This will remove a whole category of package manager
warnings about install scripts and "built" dependencies.

Most people don't need to build sharp from source, but for
those that do, a suitable method is now something like:

$ npm install package-that-depends-on-sharp
$ npm explore sharp -- npm run build

install/check.js

@@ -2,36 +2,9 @@
 // SPDX-License-Identifier: Apache-2.0
 
 try {
-  const { useGlobalLibvips, globalLibvipsVersion, log, spawnRebuild } = require('../lib/libvips');
-
-  const buildFromSource = (msg) => {
-    log(msg);
-    log('Attempting to build from source via node-gyp');
-    try {
-      const addonApi = require('node-addon-api');
-      log(`Found node-addon-api ${addonApi.version || ''}`);
-    } catch (_err) {
-      log('Please add node-addon-api to your dependencies');
-      return;
-    }
-    try {
-      const gyp = require('node-gyp');
-      log(`Found node-gyp ${gyp().version}`);
-    } catch (_err) {
-      log('Please add node-gyp to your dependencies');
-      return;
-    }
-    log('See https://sharp.pixelplumbing.com/install#building-from-source');
-    const status = spawnRebuild();
-    if (status !== 0) {
-      process.exit(status);
-    }
-  };
-
-  if (useGlobalLibvips(log)) {
-    buildFromSource(`Detected globally-installed libvips v${globalLibvipsVersion()}`);
-  } else if (process.env.npm_config_build_from_source) {
-    buildFromSource('Detected --build-from-source flag');
+  const { useGlobalLibvips } = require('../lib/libvips');
+  if (useGlobalLibvips() || process.env.npm_config_build_from_source) {
+    process.exit(1);
   }
 } catch (err) {
   const summary = err.message.split(/\n/).slice(0, 1);