Fix implicit-fallthrough warnings.

Test: make checkbuild
Bug: 112564944
Change-Id: I037abe443a47a12136744b8eb3720f75ecd9b578
diff --git a/opengl/libagl/state.cpp b/opengl/libagl/state.cpp
index 1d5def5..8bb7e83 100644
--- a/opengl/libagl/state.cpp
+++ b/opengl/libagl/state.cpp
@@ -181,7 +181,7 @@
     case GL_FOG:
     case GL_DEPTH_TEST:
         ogles_invalidate_perspective(c);
-        // fall-through...
+        [[fallthrough]];
     case GL_BLEND:
     case GL_SCISSOR_TEST:
     case GL_ALPHA_TEST: