[clang] [NFC] add DiagnosticsTestHelper decl (PR #112820)

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github-actions[bot] wrote:

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:warning: C/C++ code formatter, clang-format found issues in your code. :warning:

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git-clang-format --diff c3bbc3a57d439a039d2ea49d9b7e0f6e1c87219d a40fb059ae8bb81806cc399361c48ea5caca0336 --extensions cpp -- clang/unittests/Basic/DiagnosticTest.cpp
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View the diff from clang-format here.
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diff --git a/clang/unittests/Basic/DiagnosticTest.cpp b/clang/unittests/Basic/DiagnosticTest.cpp
index 54b32bc2bb..0cb6db686c 100644
--- a/clang/unittests/Basic/DiagnosticTest.cpp
+++ b/clang/unittests/Basic/DiagnosticTest.cpp
@@ -17,7 +17,7 @@ using namespace llvm;
 using namespace clang;
 
 namespace clang {
-   void DiagnosticsTestHelper(DiagnosticsEngine &diag);
+void DiagnosticsTestHelper(DiagnosticsEngine &diag);
 }
 
 void clang::DiagnosticsTestHelper(DiagnosticsEngine &diag) {

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https://github.com/llvm/llvm-project/pull/112820