[clang] [Clang][Sema] Reject array prvalue operands (PR #140702)

[Aaron Ballman via cfe-commits]

================
@@ -7639,6 +7639,8 @@ def warn_param_mismatched_alignment : Warning<
 
 def err_objc_object_assignment : Error<
   "cannot assign to class object (%0 invalid)">;
+def err_typecheck_array_prvalue_operand : Error<
+  "array prvalue is not permitted">;
----------------
AaronBallman wrote:

It's better than "array prvalue" but if you're coming from a C background, that's not going to look like a temporary array to you, either.

What kind of diagnostic would we get for:
```
#define X ({(int[10]){};})

void func() {
  (void)(X + 0);
}
```
IIRC there's no rvalue conversion on the statement expression result so I think that ends up being a prvalue of array type (not a decayed pointer) plus an integer, so the type information would actually be helpful.

https://github.com/llvm/llvm-project/pull/140702