Set C++ version consistently to C++ 14 (#1203)

Summary:
Pull Request resolved: https://github.com/facebook/yoga/pull/1203

~~This sets the C++ standard to C++ 17 in the working builds and Apple. GTest will stop supporting C++ 11 soon, so we need to update. C++ 14 is more embeddable, but C++ 17 support and usage should be relatively common now and the language version adds quite a bit.~~

This bumps from C++ 11 to C++ 14 in existing places where it is specified. C++ 17 allows more, and is better aligned to infra (semantics can change in std versions in suprising ways), but C++ 14 still has broader ecosystem compatibility.

Changelog: [Internal]

Reviewed By: cortinico, dmytrorykun

Differential Revision: D42285391

fbshipit-source-id: 88d7b6b8783a80b9b2e48781a2fd3d326ecd87d0

Yoga.podspec

@@ -30,7 +30,7 @@ Pod::Spec.new do |spec|
       '-fexceptions',
       '-Wall',
       '-Werror',
-      '-std=c++1y',
+      '-std=c++14',
       '-fPIC'
   ]
   spec.source_files = 'yoga/**/*.{c,h,cpp}'