Print logs to differentiate JSC and Hermes builds

Summary:
Print logs during `pod install` to clarify when Hermes is being used with RNTester and/or iOS React Native apps.

This changeset should not result in any change to the behavior of `pod install`, other than adding logs to CocoaPods' stdout.

Changelog: [Internal]

Reviewed By: cortinico

Differential Revision: D35294993

fbshipit-source-id: 55b6115d9f49c311c34ad3cb07346b2f97adcbf9

packages/rn-tester/Podfile

@@ -14,15 +14,12 @@ if USE_FRAMEWORKS
   use_frameworks!
 end
 
-if ENV['USE_HERMES'] == '1'
-  puts "Using Hermes engine"
-end
-
 def pods(options = {})
   project 'RNTesterPods.xcodeproj'
 
   fabric_enabled = true
-  puts "Building RNTester with Fabric #{fabric_enabled ? "enabled" : "disabled"}."
+  hermes_enabled = ENV['USE_HERMES'] == '1'
+  puts "Building RNTester with Fabric #{fabric_enabled ? "enabled" : "disabled"}.#{hermes_enabled ? " Using Hermes engine." : ""}"
 
   prefix_path = "../.."
 
@@ -34,7 +31,7 @@ def pods(options = {})
   use_react_native!(
     path: prefix_path,
     fabric_enabled: fabric_enabled,
-    hermes_enabled: ENV['USE_HERMES'] == '1',
+    hermes_enabled: hermes_enabled,
     app_path: "#{Dir.pwd}",
     config_file_dir: "#{Dir.pwd}/node_modules",
   )

scripts/react_native_pods.rb

@@ -111,9 +111,11 @@ def use_react_native! (options={})
   if hermes_enabled
     pod 'React-hermes', :path => "#{prefix}/ReactCommon/hermes"
     if ENV['BUILD_HERMES_SOURCE'] == '1'
+      Pod::UI.puts "[Hermes] Building Hermes from source"
       hermes_source_path = downloadAndConfigureHermesSource(prefix)
       pod 'hermes-engine', :path => "#{hermes_source_path}/hermes-engine.podspec"
     else
+      Pod::UI.warn "[Hermes] Installing Hermes from CocoaPods. The `hermes-engine` pod has been deprecated and will not see future updates."
       pod 'hermes-engine', '~> 0.11.0'
     end
     pod 'libevent', '~> 2.1.12'