VideoCore: Unify interface to OpenGL and SW rasterizers

This removes explicit checks sprinkled all over the codebase to instead
just have the SW rasterizer expose an implementation with no-ops for
most operations.

src/video_core/swrasterizer.cpp

@@ -0,0 +1,16 @@
+// Copyright 2015 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#include "video_core/clipper.h"
+#include "video_core/swrasterizer.h"
+
+namespace VideoCore {
+
+void SWRasterizer::AddTriangle(const Pica::Shader::OutputVertex& v0,
+        const Pica::Shader::OutputVertex& v1,
+        const Pica::Shader::OutputVertex& v2) {
+    Pica::Clipper::ProcessTriangle(v0, v1, v2);
+}
+
+}