[clang] [clang] Make serenity.cpp tests pass on clang-with-thin-lto-ubuntu (PR #192231)

[Lucas Chollet via cfe-commits]

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@@ -259,7 +259,7 @@
 // RUN: %clang --target=x86_64-unknown-serenity -flto %s -### 2>&1 \
 // RUN:   | FileCheck %s --check-prefix=LTO_FULL
 // LTO_FULL: "-plugin-opt=
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LucasChollet wrote:

Yes, when using thin lto `"-plugin-opt=thinlto"` is preceded by `"-plugin-opt=mcpu=`, so the first line would match the `mcpu` and the second would raise an error on the `thinlto` part.

https://github.com/llvm/llvm-project/pull/192231