Add CMake option to select OpenGL ES 2.0 or 3.0

Change-Id: I7931c771755419c64963f531eebca7634e647eeb
Add x86_64 to list of archs for iOS simulator

Most new Macs and iOS devices are 64-bit now, so make it a default.

Change-Id: I4dd8a49557ad08f7bfd495f1517d53eb92eef297
Merge topic 'basic-gles3-support' into master

7eaad015 Add x86_64 to list of archs for iOS simulator
72dfcc38 Add CMake option to select OpenGL ES 2.0 or 3.0