[perl #127908] [NativeCall] spurious warnings for type 'int'

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# New Ticket Created by  David Warring 
# Please include the string:  [perl #127908]
# in the subject line of all future correspondence about this issue. 
# <URL: https://rt.perl.org/Ticket/Display.html?id=127908 >


Consider:

$ perl6 -v
This is Rakudo version 2016.03-124-g4b0e5bd built on MoarVM version 
2016.03-108-gca1a21a
implementing Perl 6.c.
$ $ perl6 -e'use NativeCall; our sub abs(int $c) returns int is native { * }'
Potential difficulties:
    In 'abs' routine declaration - Not an accepted NativeCall type for 
parameter [1] $c : int
     --> For Numerical type, use the appropriate int32/int64/num64...
    at -e:1
    ------>  abs(int $c) returns int is native { * }⏏<EOL>
    The returning type of 'abs' --> int is erroneous. You should not return a 
non NativeCall supported type (like Int inplace of int32), truncating errors 
can appear with different architectures
    at -e:1
    ------>  abs(int $c) returns int is native { * }⏏<EOL>

But 'int' is a standard C type that is in widespread use. For example the 
definition of abs(), from stdlib.h is: 

/* Return the absolute value of X.  */
extern int abs (int __x) __THROW __attribute__ ((__const__)) __wur;