radeonsi: implement EXT_window_rectangles

Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
diff --git a/docs/relnotes/18.3.0.html b/docs/relnotes/18.3.0.html
index 786145a..ac2cc1e 100644
--- a/docs/relnotes/18.3.0.html
+++ b/docs/relnotes/18.3.0.html
@@ -52,6 +52,7 @@
 
 <ul>
 <li>GL_AMD_framebuffer_multisample_advanced on radeonsi.</li>
+<li>GL_EXT_window_rectangles on radeonsi.</li>
 </ul>
 
 <h2>Bug fixes</h2>