[clang] [clang-tools-extra] Fix OOM in FormatDiagnostic (PR #108187)

[Vakhurin Sergei via cfe-commits]

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@@ -0,0 +1,41 @@
+// RUN: %clang_cc1 -fallow-pch-with-compiler-errors -std=c++20 -x c++-header -emit-pch %s -o %t -verify
+// RUN: %clang_cc1 -fallow-pch-with-compiler-errors -std=c++20 -include-pch %t %s -verify
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igelbox wrote:

In the `main` branch it didn't fail but simply hangs. Better than nothing though.

https://github.com/llvm/llvm-project/pull/108187