[perl #131925] [BUG] [REGEX] Smartmatch against `m//` operator mishandles junctions

[Sam S. via RT]

<smls>        bisectable6: say <a b>.any ~~ m/a/;
<bisectable6> smls, On both starting points (old=2015.12 new=e3e29c5)
              the exit code is 0 and the output is identical as well
<bisectable6> smls, Output on both points: «False»