Rasterizer discard implementation

Implemented rasterizer discard by not using the SetupRoutine
and always returning 0 when rasterizer discard is enabled.
Also guarded all clear calls with a check for rasterizer
discard. Passes all rasterizer discard related dEQP tests.

Change-Id: I1e5c107e3dba550f7a5b01eb302ff51bdac303dc
Reviewed-on: https://swiftshader-review.googlesource.com/4876
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
diff --git a/src/Renderer/SetupProcessor.cpp b/src/Renderer/SetupProcessor.cpp
index 34b11be..6d4d7cb 100644
--- a/src/Renderer/SetupProcessor.cpp
+++ b/src/Renderer/SetupProcessor.cpp
@@ -89,6 +89,7 @@
 		state.pointSizeRegister = 0xF;   // No vertex point size
 
 		state.multiSample = context->getMultiSampleCount();
+		state.rasterizerDiscard = context->rasterizerDiscard;
 
 		if(context->vertexShader)
 		{