Shader: Initial implementation of x86_x64 JIT compiler for Pica vertex shaders.

- Config: Add an option for selecting to use shader JIT or interpreter.
- Qt: Add a menu option for enabling/disabling the shader JIT.

src/core/settings.h

@@ -53,6 +53,7 @@ struct Values {
 
     // Renderer
     bool use_hw_renderer;
+    bool use_shader_jit;
 
     float bg_red;
     float bg_green;