Clang 11 upgrade: fix cast size warnings in bounds.c test

[kkjeer]

In the typechecking/bounds.c test, lines 568-578 involve casting _Array_ptr<int> types to integer types. With changes introduced in clang 11, casts to a smaller integer type result in a warning: "cast to smaller integer type 'T' from '_Array_ptr'" where T is an integer type.

// byte_count
short int t20 : byte_count(5 * sizeof(int)) = (short int)a1;
int t21 : byte_count(5 * sizeof(int)) = (int)a1;
long int t22 : byte_count(5 * sizeof(int)) = (long int)a1;
unsigned long int t23 : byte_count(5 * sizeof(int)) = (unsigned long int) a1;
enum E1 t24 : byte_count(8) = EnumVal1;

// bounds
int t25 : bounds(a1, a1 + 5) = (int)a1;
long int t26 : bounds(a1, a1 + 5) = (int)a1;
unsigned long int t27 : bounds(a1, a1 + 5) = (int)a1;
enum E1 t28 : bounds(a1, a1 + 5) = (int)a1;

On different platforms, these integer types can have different sizes, so these tests should expect the "cast to smaller integer type" warning only on certain platforms.