Fix OSX retina display support.
Fix OSX retina display support.

Change-Id: I712b089c36e9c696c44a8d99a3d21819798a6142
Reviewed-on: https://swiftshader-review.googlesource.com/4430
Reviewed-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>
Tested-by: Nicolas Capens <0612353e1fcebbfd4b302d9337447ca0cdfa9122@google.com>

bkaradzic/SwiftShader,bkaradzic/SwiftShader,google/swiftshader,google/swiftshader,google/swiftshader,bkaradzic/SwiftShader,bkaradzic/SwiftShader,bkaradzic/SwiftShader