test-sizeof: show that a small 64 field is not enough to force the enum to be 64 bits

On both 32 and 64 bits, the result is:
enum Enum → 32 bits, unsigned
enum BigEnum → 32 bits, unsigned
enum BigEnum2 → 64 bits, unsigned
big_enum2_pos → 4
big_enum2_neg → 8

The last two lines show that even if the enum is 64 bit, and the field of an
enum is defined with UINT64_C(), the field can still be smaller.

src/test/test-sizeof.c

@@ -26,7 +26,12 @@ enum Enum {
 };
 
 enum BigEnum {
-        big_enum_value = UINT64_C(-1),
+        big_enum_value = UINT64_C(1),
+};
+
+enum BigEnum2 {
+        big_enum2_pos = UINT64_C(1),
+        big_enum2_neg = UINT64_C(-1),
 };
 
 int main(void) {
@@ -55,6 +60,10 @@ int main(void) {
 
         info(enum Enum);
         info(enum BigEnum);
+        info(enum BigEnum2);
+        assert_cc(sizeof(enum BigEnum2) == 8);
+        printf("big_enum2_pos → %zu\n", sizeof(big_enum2_pos));
+        printf("big_enum2_neg → %zu\n", sizeof(big_enum2_neg));
 
         return 0;
 }