add note about comptime hash map

src/lang.zig

@@ -643,7 +643,10 @@ pub const Lang = struct {
                 // in a variable because then that variable must be comptime.
 
                 // the drawback of this approach is that our emitted code is basically linear
-                // because we don't use the hashmap anymore. maybe #5359 can help.
+                // because we don't use the hashmap anymore.
+                //
+                // Attempting to use ComptimeHashMap hits compiler bugs and I'm
+                // not sure if we can map strings to *types* in it.
 
                 if (std.mem.eql(u8, &lowered_command_name, command_string)) {
                     found = true;