[perl #116643] [BUG] Null PMC access when declaring operator with a backslash in Rakudo

[Christian Bartolomaeus via RT]

On Moar and on JVM all of those declarations run fine. On Parrot the errors are 
still the same. I added tests (fudged for Parrot) for two of the different 
declarations to S06-operator-overloading/sub.t with the following commit: 
https://github.com/perl6/roast/commit/dea36c4818