LibGL: Implement glDrawBuffer

Author: https://github.com/sunverwerth
Commit: 7cbaaf8366
Pull-request: https://github.com/SerenityOS/serenity/pull/9713
Reviewed-by: https://github.com/Quaker762 ✅

Userland/Libraries/LibGL/SoftwareRasterizer.h

@@ -44,6 +44,7 @@ struct RasterizerOptions {
     GLboolean fog_enabled { false };
     GLfloat fog_start { 0.0f };
     GLfloat fog_end { 1.0f };
+    GLenum draw_buffer { GL_BACK };
 };
 
 class SoftwareRasterizer final {