gl_VertexID implementation

This cl implements support for gl_VertexID.

Passes the functional.shaders.builtin_variable.vertex_id test.

Change-Id: I5550e3ecba30e29f1e38ace608d730833a1e9598
Reviewed-on: https://swiftshader-review.googlesource.com/10958
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>

src/Shader/VertexProgram.hpp

diff --git a/src/Shader/VertexProgram.hpp b/src/Shader/VertexProgram.hpp
index bcf4a20..b537af3 100644
--- a/src/Shader/VertexProgram.hpp
+++ b/src/Shader/VertexProgram.hpp
@@ -56,14 +56,15 @@
 		Int4 enableLeave;
 
 		Int instanceID;
+		Int4 vertexID;
 
 		typedef Shader::DestinationParameter Dst;
 		typedef Shader::SourceParameter Src;
 		typedef Shader::Control Control;
 		typedef Shader::Usage Usage;
 
-		void pipeline() override;
-		void program();
+		void pipeline(UInt &index) override;
+		void program(UInt &index);
 		void passThrough();
 
 		Vector4f fetchRegister(const Src &src, unsigned int offset = 0);