Implement an OpenGL 2.1 prototype. Bug 18962347 Change-Id: I9a7b07647b1b3f561dd9e4597670e63641b155a8 Reviewed-on: https://swiftshader-review.googlesource.com/1810 Reviewed-by: Nicolas Capens <capn@google.com> Tested-by: Nicolas Capens <capn@google.com>