st/mesa: properly encode OES_geometry_shader requirement

Since the extension was added, we grew a cap to expose the number of
invocations. Use it to prevent geometry shaders from being spuriously
exposed.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10569>

src/mesa/state_tracker/st_extensions.c

@@ -1293,13 +1293,11 @@ void st_init_extensions(struct pipe_screen *screen,
       extensions->ARB_tessellation_shader = GL_TRUE;
    }
 
-   /* What this is really checking for is the ability to support multiple
-    * invocations of a geometry shader. There is no separate cap for that, so
-    * we check the GLSLVersion.
-    */
+   /* OES_geometry_shader requires instancing */
    if ((GLSLVersion >= 400 || ESSLVersion >= 310) &&
        screen->get_shader_param(screen, PIPE_SHADER_GEOMETRY,
-                                PIPE_SHADER_CAP_MAX_INSTRUCTIONS) > 0) {
+                                PIPE_SHADER_CAP_MAX_INSTRUCTIONS) > 0 &&
+       consts->MaxGeometryShaderInvocations >= 32) {
       extensions->OES_geometry_shader = GL_TRUE;
    }