[clang] [Clang] Fix assertion when __block is used on global variables in C mode (PR #194856)

[Aaron Ballman via cfe-commits]

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@@ -0,0 +1,11 @@
+// RUN: %clang_cc1 -fblocks -fsyntax-only -verify %s
+
+ at interface MyClass {
+    // expected-warning at -1 {{class 'MyClass' defined without specifying a base class}}
+    // expected-note at -2 {{add a super class to fix this problem}}
+    __block int _myIvar;
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AaronBallman wrote:

The diagnostic we emit elsewhere says this is only allowed on local variables, but this isn't a local variable.

https://github.com/llvm/llvm-project/pull/194856