[clang] [Clang] Update missing varargs arg extension warnings (PR #84520)

[via cfe-commits]

zibi2 wrote:

@Sirraide, I noticed the following build issue when new compiler with this change (bootstrap compiler)  is being used to build one of the files for `clangd`:

```
.../clang-tools-extra/clangd/unittests/FindTargetTests.cpp:430:29: error: passing no argument for the '...' parameter of a variadic macro is a C++20 extension [-Werror,-Wc++20-extensions]
  430 |   EXPECT_DECLS("AutoTypeLoc");
      |                             ^
.../clang-tools-extra/clangd/unittests/FindTargetTests.cpp:98:9: note: macro 'EXPECT_DECLS' defined here
   98 | #define EXPECT_DECLS(NodeType, ...)                                            \
      |         ^
```

Do you have suggestion how to fix it or even better provie the fix?
Thank you,
Zibi

https://github.com/llvm/llvm-project/pull/84520