glInstanceID implementation

Implementation attempt for glInstanceID.
Related dEQP tests pass.

Change-Id: I6391699a127cc7c159a2a64e3ffeaa528b611f97
Reviewed-on: https://swiftshader-review.googlesource.com/3412
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>
diff --git a/src/Shader/VertexRoutine.cpp b/src/Shader/VertexRoutine.cpp
index 94bbdeb..61bca55 100644
--- a/src/Shader/VertexRoutine.cpp
+++ b/src/Shader/VertexRoutine.cpp
@@ -52,6 +52,10 @@
 			Registers r(shader);
 			r.data = data;
 			r.constants = *Pointer<Pointer<Byte> >(data + OFFSET(DrawData,constants));
+			if(shader->instanceIdDeclared)
+			{
+				r.instanceID = *Pointer<Int>(data + OFFSET(DrawData, instanceID));
+			}
 
 			Do
 			{