Add C++ and standard v14 settings.

Summary:
This PR adds the C++ stdlib to the linker flags and sets the C++ standard that’s used to v14.

I have tested this with my app, without it any CP build would fail unless users add those flags to the generated projects themselves.

/cc grabbou
Closes https://github.com/facebook/react-native/pull/7800

Differential Revision: D3360421

fbshipit-source-id: 0a80030dd255f073a201acc6e1c846be114c2c2a

React.podspec

@@ -32,6 +32,8 @@ Pod::Spec.new do |s|
     ss.source_files        = "React/**/*.{c,h,m,mm,S}"
     ss.exclude_files       = "**/__tests__/*", "IntegrationTests/*"
     ss.frameworks          = "JavaScriptCore"
+    ss.libraries           = "stdc++"
+    ss.pod_target_xcconfig = { "CLANG_CXX_LANGUAGE_STANDARD" => "c++14" }
   end
 
   s.subspec 'ART' do |ss|