iOS: Use pre-built hermesc if available (#33827)

Summary:
Use pre-built hermesc if available by generating a ImportHermesc.cmake file that points to the hermesc binary. Recent `react-native` releases should have hermesc available in sdks/hermesc.

Hermes build scripts have been updated to support a `HERMES_OVERRIDE_HERMESC_PATH` envvar which can point to this generated ImportHermesc.cmake file.

Pull Request resolved: https://github.com/facebook/react-native/pull/33827

Changelog:
[iOS] [Changed] - Use pre-built HermesC if available in current React Native release

Reviewed By: cortinico

Differential Revision: D36024615

fbshipit-source-id: 476569f73309f9bd142f28cb02d1f7d57b6cbc6a

scripts/hermes/hermes-utils.js

@@ -18,6 +18,12 @@ const HERMES_DIR = path.join(SDKS_DIR, 'hermes');
 const HERMES_TAG_FILE_PATH = path.join(SDKS_DIR, '.hermesversion');
 const HERMES_TARBALL_BASE_URL = 'https://github.com/facebook/hermes/tarball/';
 const HERMES_TARBALL_DOWNLOAD_DIR = path.join(SDKS_DIR, 'download');
+const MACOS_BIN_DIR = path.join(SDKS_DIR, 'hermesc', 'osx-bin');
+const MACOS_HERMESC_PATH = path.join(MACOS_BIN_DIR, 'hermesc');
+const MACOS_IMPORT_HERMESC_PATH = path.join(
+  MACOS_BIN_DIR,
+  'ImportHermesc.cmake',
+);
 
 function prepareFileSystem() {
   if (!fs.existsSync(SDKS_DIR)) {
@@ -135,11 +141,31 @@ function copyBuildScripts() {
   );
 }
 
+function shouldUsePrebuiltHermesC(os) {
+  if (os === 'macos') {
+    return fs.existsSync(MACOS_HERMESC_PATH);
+  }
+
+  return false;
+}
+
+function configureMakeForPrebuiltHermesC() {
+  const IMPORT_HERMESC_TEMPLATE = `add_executable(native-hermesc IMPORTED)
+set_target_properties(native-hermesc PROPERTIES
+  IMPORTED_LOCATION "${MACOS_HERMESC_PATH}"
+  )`;
+
+  fs.mkdirSync(MACOS_BIN_DIR, {recursive: true});
+  fs.writeFileSync(MACOS_IMPORT_HERMESC_PATH, IMPORT_HERMESC_TEMPLATE);
+}
+
 module.exports = {
+  configureMakeForPrebuiltHermesC,
   copyBuildScripts,
   downloadHermesTarball,
   expandHermesTarball,
   getHermesTagSHA,
   readHermesTag,
   setHermesTag,
+  shouldUsePrebuiltHermesC,
 };

scripts/hermes/prepare-hermes-for-build.js

@@ -14,11 +14,18 @@
  * iOS build pipeline on macOS.
  */
 const {
+  configureMakeForPrebuiltHermesC,
   copyBuildScripts,
   downloadHermesTarball,
   expandHermesTarball,
+  shouldUsePrebuiltHermesC,
 } = require('./hermes-utils');
 
 downloadHermesTarball();
 expandHermesTarball();
 copyBuildScripts();
+
+if (shouldUsePrebuiltHermesC('macos')) {
+  console.log('[Hermes] Using pre-built HermesC');
+  configureMakeForPrebuiltHermesC();
+}