[reg] fix Issue 13084 - ModuleInfo.opApply delegate expects immutable parameter

https://issues.dlang.org/show_bug.cgi?id=13084

Also requires https://github.com/D-Programming-Language/druntime/pull/886

The changes are pretty self-explanatory, it avoids breaking ModuleInfo code because it is now immutable.
Also, that comment in the middle of the expression will break DDMD.  Please at least move it outside the if condition.