[perl #131181] [BUG] "Invalid BUILD_LEAST_DERIVED plan" when `but`-ing a role with native-int attribute

[jn...@jnthn.net via RT]

On Thu, 20 Apr 2017 07:53:23 -0700, c...@zoffix.com wrote:
> 14:51   Zoffix  m: $ = 42 but role { has int $!x  }
> 14:51   camelia         rakudo-moar 277b6e: ( no output )
> 14:51   Zoffix  m: $ = 42 but role { has Int $!x = 42  }
> 14:51   camelia         rakudo-moar 277b6e: ( no output )
> 14:51   Zoffix  m: $ = 42 but role { has int $!x = 42 }
> 14:51   camelia         rakudo-moar 277b6e: OUTPUT: «Invalid
> BUILD_LEAST_DERIVED plan␤  in block <unit> at <tmp> line 1␤␤»

Fixed (plus the num and str cases too) and test added to 
S12-attributes/defaults.t.