[BUG] CN crashes if spec arg list does not match function

[peterohanley]

Summary

Rather than print location information CN crashes on this input.

Bug

void f(char *p);
/*@ spec f(pointer p, i32 a);
    requires true;
    ensures true;
@*/

% cn arg_mismatch.c                           
cn: internal error, uncaught exception:
    Invalid_argument("List.combine")
    Raised at Stdlib.invalid_arg in file "stdlib.ml", line 30, characters 20-45
    Called from Stdlib__List.combine in file "list.ml", line 305, characters 36-49
    Called from Dune__exe__Core_to_mucore.normalise_fun_map_decl in file "backend/cn/core_to_mucore.ml", line 1328, characters 19-74
...

Acceptance Criteria

Print a normal syntax error with location information.

Do

• assign issue to a Milestone
• define acceptance criteria
• add appropriate labels
• Check the list lengths before calling list combine