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/VertexShader.cpp b/src/Shader/VertexShader.cpp
index 3b888d7..7bb7f0a 100644
--- a/src/Shader/VertexShader.cpp
+++ b/src/Shader/VertexShader.cpp
@@ -41,6 +41,7 @@
 			memcpy(input, vs->input, sizeof(input));
 			positionRegister = vs->positionRegister;
 			pointSizeRegister = vs->pointSizeRegister;
+			instanceIdDeclared = vs->instanceIdDeclared;
 			usedSamplers = vs->usedSamplers;
 
 			optimize();