[clang] [clang-tools-extra] [Clang] Add support for the C `defer` TS (PR #162848)

[Aaron Ballman via cfe-commits]

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@@ -0,0 +1,5 @@
+// RUN: %clang_cc1 -fsyntax-only -verify %s
+// RUN: %clang_cc1 -fsyntax-only -verify -fdefer-ts %s
+
+// expected-no-diagnostics
+int defer;
----------------
AaronBallman wrote:

```suggestion
int _Defer;
```
otherwise we're not testing what we think we're testing. :-) I still think it makes sense to warn about enabling the flag in C++ mode just so users don't get baffling diagnostics.


https://github.com/llvm/llvm-project/pull/162848