[perl #77562] rakudo parses /$'x'/ but STD doesn't

[Christian Bartolomaeus via RT]

Nowadays this is parsed by STD and Rakudo (on Moar, Parrot and JVM):

$ viv -c -e "/$'x'/"
 syntax OK

$ perl6 -e "/$'x'/"
$ perl6 -e "say (/$'x'/).perl"
regex (Mu: *%_) { #`(Regex|70560384) ... }

I added a test to S05-metasyntax/unknown.t with commit 
https://github.com/perl6/roast/commit/72709f1783

I'm closing this ticket now. If you think this is not solved (maybe even STD 
gets it wrong now?), please reopen.