[perl #120831] [BUG] LTA error message when declaring 'my Int a' in Rakudo

[Christian Bartolomaeus via RT]

Since the current error message looks reasonable to me (though different from 
STD's) I went ahead and added a test to S32-exceptions/misc.t with the 
following commit: https://github.com/perl6/roast/commit/5265f7d69e

But: The new error message only happens with "my Int a;". Without the semicolon 
we get the old error message.

$ perl6-m -e 'my Int a;'
===SORRY!=== Error while compiling -e
Malformed my (did you mean to declare a sigilless \a or $a?)
at -e:1
------> my Int a⏏;

$ perl6-m -e 'my Int a'
===SORRY!===
Type 'Int' is not declared. Did you mean 'int'?
at -e:1
------> my Int ⏏a
Malformed my
at -e:1
------> my Int ⏏a
    expecting any of:
        scoped declarator

$ viv -c -e 'my Int a;'
===SORRY!===
Multiple prefix constraints not yet supported at (eval) line 1:
------> my Int ⏏a;
Malformed my at (eval) line 1:
------> my Int ⏏a;
    expecting any of:
        multi_declarator
        typename
Parse failed

$ viv -c -e 'my Int a'
===SORRY!===
Multiple prefix constraints not yet supported at (eval) line 1:
------> my Int ⏏a
Malformed my at (eval) line 1:
------> my Int ⏏a
    expecting any of:
        multi_declarator
        typename
Parse failed