zig.h: Add some casts to __atomic macros to shut Clang warnings up.

This is a stupid Clang-ism:

    ❯ cat test.c
    int main() {
        int value = 42;
        int const *value_ptr = &value;
        int location;
        __atomic_store(&location, value_ptr, __ATOMIC_SEQ_CST);
    }
    ❯ gcc test.c -fsyntax-only
    ❯ clang test.c -fsyntax-only
    test.c:5:31: warning: passing 'const int *' to parameter of type 'int *' discards qualifiers [-Wincompatible-pointer-types-discards-qualifiers]
        5 |     __atomic_store(&location, value_ptr, __ATOMIC_SEQ_CST);
          |                               ^~~~~~~~~
    1 warning generated.

I have no idea why Clang doesn't define these builtins as taking const pointers
for the parameters that are only read from. Anyway, after the next zig1.wasm
update, this change should shut up these warnings that we've been seeing in CI
during bootstrap for ages.

lib/zig.h

@@ -3765,9 +3765,9 @@ typedef int zig_memory_order;
 #define zig_memory_order_acq_rel __ATOMIC_ACQ_REL
 #define zig_memory_order_seq_cst __ATOMIC_SEQ_CST
 #define zig_atomic(Type) Type
-#define zig_cmpxchg_strong(     obj, expected, desired, succ, fail, Type, ReprType) __atomic_compare_exchange(obj, &(expected), &(desired), false, succ, fail)
-#define   zig_cmpxchg_weak(     obj, expected, desired, succ, fail, Type, ReprType) __atomic_compare_exchange(obj, &(expected), &(desired),  true, succ, fail)
-#define zig_atomicrmw_xchg(res, obj, arg, order, Type, ReprType)       __atomic_exchange(obj, &(arg), &(res), order)
+#define zig_cmpxchg_strong(     obj, expected, desired, succ, fail, Type, ReprType) __atomic_compare_exchange(obj, (ReprType *)&(expected), (ReprType *)&(desired), false, succ, fail)
+#define   zig_cmpxchg_weak(     obj, expected, desired, succ, fail, Type, ReprType) __atomic_compare_exchange(obj, (ReprType *)&(expected), (ReprType *)&(desired),  true, succ, fail)
+#define zig_atomicrmw_xchg(res, obj, arg, order, Type, ReprType)       __atomic_exchange(obj, (ReprType *)&(arg), &(res), order)
 #define  zig_atomicrmw_add(res, obj, arg, order, Type, ReprType) res = __atomic_fetch_add (obj, arg, order)
 #define  zig_atomicrmw_sub(res, obj, arg, order, Type, ReprType) res = __atomic_fetch_sub (obj, arg, order)
 #define   zig_atomicrmw_or(res, obj, arg, order, Type, ReprType) res = __atomic_fetch_or  (obj, arg, order)
@@ -3776,7 +3776,7 @@ typedef int zig_memory_order;
 #define zig_atomicrmw_nand(res, obj, arg, order, Type, ReprType) res = __atomic_fetch_nand(obj, arg, order)
 #define  zig_atomicrmw_min(res, obj, arg, order, Type, ReprType) res = __atomic_fetch_min (obj, arg, order)
 #define  zig_atomicrmw_max(res, obj, arg, order, Type, ReprType) res = __atomic_fetch_max (obj, arg, order)
-#define   zig_atomic_store(     obj, arg, order, Type, ReprType)       __atomic_store     (obj, &(arg), order)
+#define   zig_atomic_store(     obj, arg, order, Type, ReprType)       __atomic_store     (obj, (ReprType *)&(arg), order)
 #define    zig_atomic_load(res, obj,      order, Type, ReprType)       __atomic_load      (obj, &(res), order)
 #undef  zig_atomicrmw_xchg_float
 #define zig_atomicrmw_xchg_float zig_atomicrmw_xchg