[clang] Add more tests for _Countof (PR #133333)

[Aaron Ballman via cfe-commits]

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@@ -121,10 +150,14 @@ void test_typedefs() {
   static_assert(_Countof(*x) == 12);
 }
 
-void test_zero_size_arrays() {
+void test_zero_size_arrays(int n) {
   int array[0]; // expected-warning {{zero size arrays are an extension}}
   static_assert(_Countof(array) == 0);
   static_assert(_Countof(int[0]) == 0); // expected-warning {{zero size arrays are an extension}}
+  int multi_array[0][n]; // expected-warning {{zero size arrays are an extension}}
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AaronBallman wrote:

Note, currently we don't issue a zero-sized array extension warning for this case: https://godbolt.org/z/78W8cr9o5 (seems like a preexisting bug)

https://github.com/llvm/llvm-project/pull/133333